diff --git a/blob.c b/blob.c
index e927f4ff..3e5b7723 100644
--- a/blob.c
+++ b/blob.c
@@ -60,17 +60,15 @@ static pic_value
 pic_blob_make_bytevector(pic_state *pic)
 {
   pic_blob *blob;
-  int k, b = 0, i;
+  size_t k, i;
+  int b = 0;
 
-  pic_get_args(pic, "i|i", &k, &b);
+  pic_get_args(pic, "k|i", &k, &b);
 
   if (b < 0 || b > 255)
     pic_errorf(pic, "byte out of range");
 
-  if (k < 0)
-    pic_errorf(pic, "make-bytevector: cannot create a bytevector of length %d", k);
-
-  blob = pic_make_blob(pic, (size_t)k);
+  blob = pic_make_blob(pic, k);
   for (i = 0; i < k; ++i) {
     blob->data[i] = (unsigned char)b;
   }
@@ -85,7 +83,7 @@ pic_blob_bytevector_length(pic_state *pic)
 
   pic_get_args(pic, "b", &bv);
 
-  return pic_int_value((int)bv->len);
+  return pic_size_value(bv->len);
 }
 
 static pic_value
@@ -118,15 +116,16 @@ static pic_value
 pic_blob_bytevector_copy_i(pic_state *pic)
 {
   pic_blob *to, *from;
-  int n, at, start, end;
+  int n;
+  size_t at, start, end;
 
-  n = pic_get_args(pic, "bib|ii", &to, &at, &from, &start, &end);
+  n = pic_get_args(pic, "bkb|kk", &to, &at, &from, &start, &end);
 
   switch (n) {
   case 3:
     start = 0;
   case 4:
-    end = (int)from->len;
+    end = from->len;
   }
 
   if (to == from && (start <= at && at < end)) {
@@ -149,23 +148,23 @@ static pic_value
 pic_blob_bytevector_copy(pic_state *pic)
 {
   pic_blob *from, *to;
-  int n, start, end, k, i = 0;
+  int n;
+  size_t start, end, i = 0;
 
-  n = pic_get_args(pic, "b|ii", &from, &start, &end);
+  n = pic_get_args(pic, "b|kk", &from, &start, &end);
 
   switch (n) {
   case 1:
     start = 0;
   case 2:
-    end = (int)from->len;
+    end = from->len;
   }
 
-  k = end - start;
+  if (end < start) {
+    pic_errorf(pic, "make-bytevector: end index must not be less than start index");
+  }
 
-  if (k < 0)
-    pic_errorf(pic, "make-bytevector: cannot create a bytevector of length %d", k);
-
-  to = pic_make_blob(pic, (size_t)k);
+  to = pic_make_blob(pic, end - start);
   while (start < end) {
     to->data[i++] = from->data[start++];
   }
@@ -210,7 +209,7 @@ pic_blob_list_to_bytevector(pic_state *pic)
 
   pic_get_args(pic, "o", &list);
 
-  blob = pic_make_blob(pic, (size_t)pic_length(pic, list));
+  blob = pic_make_blob(pic, pic_length(pic, list));
 
   data = blob->data;
 
@@ -230,15 +229,16 @@ pic_blob_bytevector_to_list(pic_state *pic)
 {
   pic_blob *blob;
   pic_value list;
-  int n, start, end, i;
+  int n;
+  size_t start, end, i;
 
-  n = pic_get_args(pic, "b|ii", &blob, &start, &end);
+  n = pic_get_args(pic, "b|kk", &blob, &start, &end);
 
   switch (n) {
   case 1:
     start = 0;
   case 2:
-    end = (int)blob->len;
+    end = blob->len;
   }
 
   list = pic_nil_value();
diff --git a/char.c b/char.c
index 98eed6f7..d9c675e7 100644
--- a/char.c
+++ b/char.c
@@ -42,9 +42,8 @@ pic_char_integer_to_char(pic_state *pic)
   static pic_value					\
   pic_char_##name##_p(pic_state *pic)			\
   {							\
-    size_t argc;					\
+    size_t argc, i;                                     \
     pic_value *argv;					\
-    size_t i;						\
     char c, d;						\
     							\
     pic_get_args(pic, "cc*", &c, &d, &argc, &argv);	\
diff --git a/codegen.c b/codegen.c
index 55bb8587..f6183278 100644
--- a/codegen.c
+++ b/codegen.c
@@ -490,7 +490,6 @@ analyze_if(analyze_state *state, pic_value obj, bool tailpos)
   switch (pic_length(pic, obj)) {
   default:
     pic_errorf(pic, "syntax error");
-    break;
   case 4:
     if_false = pic_list_ref(pic, obj, 3);
     FALLTHROUGH;
@@ -956,7 +955,7 @@ create_activation(codegen_context *cxt)
     if ((n = xh_val(xh_get_int(&regs, *var), size_t)) <= xv_size(&cxt->args) || (cxt->varg && n == xv_size(&cxt->args) + 1)) {
       /* copy arguments to capture variable area */
       cxt->code[cxt->clen].insn = OP_LREF;
-      cxt->code[cxt->clen].u.i = n;
+      cxt->code[cxt->clen].u.i = (int)n;
       cxt->clen++;
     } else {
       /* otherwise, just extend the stack */
@@ -1030,9 +1029,9 @@ pop_codegen_context(codegen_state *state)
   irep = (struct pic_irep *)pic_obj_alloc(pic, sizeof(struct pic_irep), PIC_TT_IREP);
   irep->name = state->cxt->name;
   irep->varg = state->cxt->varg;
-  irep->argc = xv_size(&state->cxt->args) + 1;
-  irep->localc = xv_size(&state->cxt->locals);
-  irep->capturec = xv_size(&state->cxt->captures);
+  irep->argc = (int)xv_size(&state->cxt->args) + 1;
+  irep->localc = (int)xv_size(&state->cxt->locals);
+  irep->capturec = (int)xv_size(&state->cxt->captures);
   irep->code = pic_realloc(pic, state->cxt->code, sizeof(pic_code) * state->cxt->clen);
   irep->clen = state->cxt->clen;
   irep->irep = pic_realloc(pic, state->cxt->irep, sizeof(struct pic_irep *) * state->cxt->ilen);
@@ -1067,7 +1066,7 @@ index_capture(codegen_state *state, pic_sym sym, int depth)
   for (i = 0; i < xv_size(&cxt->captures); ++i) {
     var = xv_get(&cxt->captures, i);
     if (*var == sym)
-      return i;
+      return (int)i;
   }
   return -1;
 }
@@ -1083,13 +1082,13 @@ index_local(codegen_state *state, pic_sym sym)
   for (i = 0; i < xv_size(&cxt->args); ++i) {
     var = xv_get(&cxt->args, i);
     if (*var == sym)
-      return i + offset;
+      return (int)(i + offset);
   }
   offset += i;
   for (i = 0; i < xv_size(&cxt->locals); ++i) {
     var = xv_get(&cxt->locals, i);
     if (*var == sym)
-      return i + offset;
+      return (int)(i + offset);
   }
   return -1;
 }
@@ -1127,7 +1126,7 @@ codegen(codegen_state *state, pic_value obj)
     name = pic_sym(pic_list_ref(pic, obj, 1));
     if ((i = index_capture(state, name, 0)) != -1) {
       cxt->code[cxt->clen].insn = OP_LREF;
-      cxt->code[cxt->clen].u.i = i + xv_size(&cxt->args) + xv_size(&cxt->locals) + 1;
+      cxt->code[cxt->clen].u.i = i + (int)xv_size(&cxt->args) + (int)xv_size(&cxt->locals) + 1;
       cxt->clen++;
       return;
     }
@@ -1173,7 +1172,7 @@ codegen(codegen_state *state, pic_value obj)
       name = pic_sym(pic_list_ref(pic, var, 1));
       if ((i = index_capture(state, name, 0)) != -1) {
         cxt->code[cxt->clen].insn = OP_LSET;
-        cxt->code[cxt->clen].u.i = i + xv_size(&cxt->args) + xv_size(&cxt->locals) + 1;
+        cxt->code[cxt->clen].u.i = i + (int)xv_size(&cxt->args) + (int)xv_size(&cxt->locals) + 1;
         cxt->clen++;
         cxt->code[cxt->clen].insn = OP_PUSHNONE;
         cxt->clen++;
@@ -1194,7 +1193,7 @@ codegen(codegen_state *state, pic_value obj)
       cxt->icapa *= 2;
       cxt->irep = pic_realloc(pic, cxt->irep, sizeof(struct pic_irep *) * cxt->icapa);
     }
-    k = cxt->ilen++;
+    k = (int)cxt->ilen++;
     cxt->code[cxt->clen].insn = OP_LAMBDA;
     cxt->code[cxt->clen].u.i = k;
     cxt->clen++;
@@ -1208,18 +1207,18 @@ codegen(codegen_state *state, pic_value obj)
     codegen(state, pic_list_ref(pic, obj, 1));
 
     cxt->code[cxt->clen].insn = OP_JMPIF;
-    s = cxt->clen++;
+    s = (int)cxt->clen++;
 
     /* if false branch */
     codegen(state, pic_list_ref(pic, obj, 3));
     cxt->code[cxt->clen].insn = OP_JMP;
-    t = cxt->clen++;
+    t = (int)cxt->clen++;
 
-    cxt->code[s].u.i = cxt->clen - s;
+    cxt->code[s].u.i = (int)cxt->clen - s;
 
     /* if true branch */
     codegen(state, pic_list_ref(pic, obj, 2));
-    cxt->code[t].u.i = cxt->clen - t;
+    cxt->code[t].u.i = (int)cxt->clen - t;
     return;
   }
   else if (sym == pic->sBEGIN) {
@@ -1267,7 +1266,7 @@ codegen(codegen_state *state, pic_value obj)
         cxt->pcapa *= 2;
         cxt->pool = pic_realloc(pic, cxt->pool, sizeof(pic_value) * cxt->pcapa);
       }
-      pidx = cxt->plen++;
+      pidx = (int)cxt->plen++;
       cxt->pool[pidx] = obj;
       cxt->code[cxt->clen].insn = OP_PUSHCONST;
       cxt->code[cxt->clen].u.i = pidx;
@@ -1376,7 +1375,7 @@ codegen(codegen_state *state, pic_value obj)
     return;
   }
   else if (sym == state->sCALL || sym == state->sTAILCALL) {
-    int len = pic_length(pic, obj);
+    int len = (int)pic_length(pic, obj);
     pic_value elt;
 
     pic_for_each (elt, pic_cdr(pic, obj)) {
@@ -1402,7 +1401,7 @@ codegen(codegen_state *state, pic_value obj)
     return;
   }
   else if (sym == state->sRETURN) {
-    int len = pic_length(pic, obj);
+    int len = (int)pic_length(pic, obj);
     pic_value elt;
 
     pic_for_each (elt, pic_cdr(pic, obj)) {
diff --git a/cont.c b/cont.c
index f010f532..4e38e8c6 100644
--- a/cont.c
+++ b/cont.c
@@ -191,7 +191,7 @@ pic_values_by_array(pic_state *pic, size_t argc, pic_value *argv)
   for (i = 0; i < argc; ++i) {
     pic->sp[i] = argv[i];
   }
-  pic->ci->retc = argc;
+  pic->ci->retc = (int)argc;
 
   return argc == 0 ? pic_none_value() : pic->sp[0];
 }
@@ -200,7 +200,7 @@ pic_value
 pic_values_by_list(pic_state *pic, pic_value list)
 {
   pic_value v;
-  size_t i;
+  int i;
 
   i = 0;
   pic_for_each (v, list) {
@@ -219,7 +219,7 @@ pic_receive(pic_state *pic, size_t n, pic_value *argv)
 
   /* take info from discarded frame */
   ci = pic->ci + 1;
-  retc = ci->retc;
+  retc = (size_t)ci->retc;
 
   for (i = 0; i < retc && i < n; ++i) {
     argv[i] = ci->fp[i];
diff --git a/dict.c b/dict.c
index 13200c08..81bdea68 100644
--- a/dict.c
+++ b/dict.c
@@ -12,11 +12,13 @@ xh_value_hash(const void *key, void *data)
 {
   union { double f; int i; } u;
   pic_value val = *(pic_value *)key;
-  int hash;
+  int hash, vtype;
 
   UNUSED(data);
 
-  switch (pic_vtype(val)) {
+  vtype = pic_vtype(val);
+
+  switch (vtype) {
   default:
     hash = 0;
     break;
@@ -31,11 +33,11 @@ xh_value_hash(const void *key, void *data)
     hash = pic_int(val);
     break;
   case PIC_VTYPE_HEAP:
-    hash = (int)pic_ptr(val);
+    hash = (int)(intptr_t)pic_ptr(val);
     break;
   }
 
-  return hash + (int)pic_vtype(val);
+  return hash + vtype;
 }
 
 static int
@@ -213,7 +215,7 @@ pic_dict_dictionary_size(pic_state *pic)
 
   pic_get_args(pic, "d", &dict);
 
-  return pic_int_value((int)pic_dict_size(pic, dict));
+  return pic_size_value(pic_dict_size(pic, dict));
 }
 
 static pic_value
diff --git a/error.c b/error.c
index b25cbb42..3b462969 100644
--- a/error.c
+++ b/error.c
@@ -90,7 +90,8 @@ void
 pic_push_try(pic_state *pic, struct pic_escape *escape)
 {
   struct pic_proc *cont, *handler;
-  size_t xp_len, xp_offset;
+  size_t xp_len;
+  ptrdiff_t xp_offset;
 
   cont = pic_make_econt(pic, escape);
 
@@ -99,7 +100,7 @@ pic_push_try(pic_state *pic, struct pic_escape *escape)
   pic_attr_set(pic, pic_obj_value(handler), "@@escape", pic_obj_value(cont));
 
   if (pic->xp >= pic->xpend) {
-    xp_len = (pic->xpend - pic->xpbase) * 2;
+    xp_len = (size_t)(pic->xpend - pic->xpbase) * 2;
     xp_offset = pic->xp - pic->xpbase;
     pic->xpbase = pic_realloc(pic, pic->xpbase, sizeof(struct pic_proc *) * xp_len);
     pic->xp = pic->xpbase + xp_offset;
@@ -198,12 +199,13 @@ pic_error_with_exception_handler(pic_state *pic)
 {
   struct pic_proc *handler, *thunk;
   pic_value val;
-  size_t xp_len, xp_offset;
+  size_t xp_len;
+  ptrdiff_t xp_offset;
 
   pic_get_args(pic, "ll", &handler, &thunk);
 
   if (pic->xp >= pic->xpend) {
-    xp_len = (pic->xpend - pic->xpbase) * 2;
+    xp_len = (size_t)(pic->xpend - pic->xpbase) * 2;
     xp_offset = pic->xp - pic->xpbase;
     pic->xpbase = pic_realloc(pic, pic->xpbase, sizeof(struct pic_proc *) * xp_len);
     pic->xp = pic->xpbase + xp_offset;
diff --git a/include/picrin/irep.h b/include/picrin/irep.h
index c6e5befb..fe924bbc 100644
--- a/include/picrin/irep.h
+++ b/include/picrin/irep.h
@@ -52,8 +52,8 @@ struct pic_code {
     int i;
     char c;
     struct {
-      short depth;
-      short idx;
+      int depth;
+      int idx;
     } r;
   } u;
 };
diff --git a/include/picrin/pair.h b/include/picrin/pair.h
index 16c61863..d489b765 100644
--- a/include/picrin/pair.h
+++ b/include/picrin/pair.h
@@ -57,7 +57,7 @@ pic_value pic_list5(pic_state *, pic_value, pic_value, pic_value, pic_value, pic
 pic_value pic_list6(pic_state *, pic_value, pic_value, pic_value, pic_value, pic_value, pic_value);
 pic_value pic_list7(pic_state *, pic_value, pic_value, pic_value, pic_value, pic_value, pic_value, pic_value);
 pic_value pic_list_by_array(pic_state *, size_t, pic_value *);
-pic_value pic_make_list(pic_state *, int, pic_value);
+pic_value pic_make_list(pic_state *, size_t, pic_value);
 
 #define pic_for_each(var, list)                                 \
   pic_for_each_helper_(var, GENSYM(tmp), list)
@@ -69,7 +69,7 @@ pic_value pic_make_list(pic_state *, int, pic_value);
 #define pic_push(pic, item, place) (place = pic_cons(pic, item, place))
 #define pic_pop(pic, place) (place = pic_cdr(pic, place))
 
-int pic_length(pic_state *, pic_value);
+size_t pic_length(pic_state *, pic_value);
 pic_value pic_reverse(pic_state *, pic_value);
 pic_value pic_append(pic_state *, pic_value, pic_value);
 
@@ -88,9 +88,9 @@ pic_value pic_cadr(pic_state *, pic_value);
 pic_value pic_cdar(pic_state *, pic_value);
 pic_value pic_cddr(pic_state *, pic_value);
 
-pic_value pic_list_tail(pic_state *, pic_value, int);
-pic_value pic_list_ref(pic_state *, pic_value, int);
-void pic_list_set(pic_state *, pic_value, int, pic_value);
+pic_value pic_list_tail(pic_state *, pic_value, size_t);
+pic_value pic_list_ref(pic_state *, pic_value, size_t);
+void pic_list_set(pic_state *, pic_value, size_t, pic_value);
 pic_value pic_list_copy(pic_state *, pic_value);
 
 #if defined(__cplusplus)
diff --git a/include/picrin/value.h b/include/picrin/value.h
index 37dd58c0..d0c1dbe3 100644
--- a/include/picrin/value.h
+++ b/include/picrin/value.h
@@ -189,6 +189,7 @@ static inline pic_value pic_undef_value();
 static inline pic_value pic_obj_value(void *);
 static inline pic_value pic_float_value(double);
 static inline pic_value pic_int_value(int);
+static inline pic_value pic_size_value(size_t);
 static inline pic_value pic_sym_value(pic_sym);
 static inline pic_value pic_char_value(char c);
 static inline pic_value pic_none_value();
@@ -323,6 +324,17 @@ pic_bool_value(bool b)
   return v;
 }
 
+static inline pic_value
+pic_size_value(size_t s)
+{
+  if (sizeof(unsigned) < sizeof(size_t)) {
+    if (s > (size_t)INT_MAX) {
+      return pic_float_value(s);
+    }
+  }
+  return pic_int_value((int)s);
+}
+
 #if PIC_NAN_BOXING
 
 static inline pic_value
diff --git a/number.c b/number.c
index 2ed93a79..88db88d6 100644
--- a/number.c
+++ b/number.c
@@ -162,9 +162,8 @@ pic_number_nan_p(pic_state *pic)
   static pic_value					\
   pic_number_##name(pic_state *pic)			\
   {							\
-    size_t argc;					\
+    size_t argc, i;                                     \
     pic_value *argv;					\
-    size_t i;						\
     double f,g;						\
     							\
     pic_get_args(pic, "ff*", &f, &g, &argc, &argv);	\
@@ -198,9 +197,8 @@ DEFINE_ARITH_CMP(>=, ge)
   static pic_value                                              \
   pic_number_##name(pic_state *pic)                             \
   {                                                             \
-    size_t argc;                                                \
+    size_t argc, i;                                             \
     pic_value *argv;                                            \
-    size_t i;                                                   \
     double f;                                                   \
     bool e = true;                                              \
                                                                 \
@@ -230,9 +228,8 @@ DEFINE_ARITH_OP(*, mul, 1)
   static pic_value                                                      \
   pic_number_##name(pic_state *pic)                                     \
   {                                                                     \
-   size_t argc;                                                         \
+    size_t argc, i;                                                     \
    pic_value *argv;                                                     \
-   size_t i;                                                            \
    double f;                                                            \
    bool e;                                                              \
                                                                         \
diff --git a/pair.c b/pair.c
index ee2263c7..b662534a 100644
--- a/pair.c
+++ b/pair.c
@@ -172,10 +172,10 @@ pic_list_by_array(pic_state *pic, size_t c, pic_value *vs)
 }
 
 pic_value
-pic_make_list(pic_state *pic, int k, pic_value fill)
+pic_make_list(pic_state *pic, size_t k, pic_value fill)
 {
   pic_value list;
-  int i;
+  size_t i;
 
   list = pic_nil_value();
   for (i = 0; i < k; ++i) {
@@ -185,10 +185,10 @@ pic_make_list(pic_state *pic, int k, pic_value fill)
   return list;
 }
 
-int
+size_t
 pic_length(pic_state *pic, pic_value obj)
 {
-  int c = 0;
+  size_t c = 0;
 
   if (! pic_list_p(obj)) {
     pic_errorf(pic, "length: expected list, but got ~s", obj);
@@ -375,7 +375,7 @@ pic_cddr(pic_state *pic, pic_value v)
 }
 
 pic_value
-pic_list_tail(pic_state *pic, pic_value list, int i)
+pic_list_tail(pic_state *pic, pic_value list, size_t i)
 {
   while (i-- > 0) {
     list = pic_cdr(pic, list);
@@ -384,13 +384,13 @@ pic_list_tail(pic_state *pic, pic_value list, int i)
 }
 
 pic_value
-pic_list_ref(pic_state *pic, pic_value list, int i)
+pic_list_ref(pic_state *pic, pic_value list, size_t i)
 {
   return pic_car(pic, pic_list_tail(pic, list, i));
 }
 
 void
-pic_list_set(pic_state *pic, pic_value list, int i, pic_value obj)
+pic_list_set(pic_state *pic, pic_value list, size_t i, pic_value obj)
 {
   pic_pair_ptr(pic_list_tail(pic, list, i))->car = obj;
 }
@@ -533,10 +533,10 @@ pic_pair_list_p(pic_state *pic)
 static pic_value
 pic_pair_make_list(pic_state *pic)
 {
-  int i;
+  size_t i;
   pic_value fill = pic_none_value();
 
-  pic_get_args(pic, "i|o", &i, &fill);
+  pic_get_args(pic, "k|o", &i, &fill);
 
   return pic_make_list(pic, i, fill);
 }
@@ -559,7 +559,7 @@ pic_pair_length(pic_state *pic)
 
   pic_get_args(pic, "o", &list);
 
-  return pic_int_value(pic_length(pic, list));
+  return pic_size_value(pic_length(pic, list));
 }
 
 static pic_value
@@ -596,9 +596,9 @@ static pic_value
 pic_pair_list_tail(pic_state *pic)
 {
   pic_value list;
-  int i;
+  size_t i;
 
-  pic_get_args(pic, "oi", &list, &i);
+  pic_get_args(pic, "ok", &list, &i);
 
   return pic_list_tail(pic, list, i);
 }
@@ -607,9 +607,9 @@ static pic_value
 pic_pair_list_ref(pic_state *pic)
 {
   pic_value list;
-  int i;
+  size_t i;
 
-  pic_get_args(pic, "oi", &list, &i);
+  pic_get_args(pic, "ok", &list, &i);
 
   return pic_list_ref(pic, list, i);
 }
@@ -618,9 +618,9 @@ static pic_value
 pic_pair_list_set(pic_state *pic)
 {
   pic_value list, obj;
-  int i;
+  size_t i;
 
-  pic_get_args(pic, "oio", &list, &i, &obj);
+  pic_get_args(pic, "oko", &list, &i, &obj);
 
   pic_list_set(pic, list, i, obj);
 
@@ -641,26 +641,26 @@ static pic_value
 pic_pair_map(pic_state *pic)
 {
   struct pic_proc *proc;
-  size_t argc;
+  size_t argc, i;
   pic_value *args;
-  int i;
-  pic_value cars, ret;
+  pic_value arg, ret;
 
   pic_get_args(pic, "l*", &proc, &argc, &args);
 
   ret = pic_nil_value();
   do {
-    cars = pic_nil_value();
-    for (i = argc - 1; i >= 0; --i) {
+    arg = pic_nil_value();
+    for (i = 0; i < argc; ++i) {
       if (! pic_pair_p(args[i])) {
         break;
       }
-      cars = pic_cons(pic, pic_car(pic, args[i]), cars);
+      pic_push(pic, pic_car(pic, args[i]), arg);
       args[i] = pic_cdr(pic, args[i]);
     }
-    if (i >= 0)
+    if (i != argc) {
       break;
-    ret = pic_cons(pic, pic_apply(pic, proc, cars), ret);
+    }
+    pic_push(pic, pic_apply(pic, proc, pic_reverse(pic, arg)), ret);
   } while (1);
 
   return pic_reverse(pic, ret);
@@ -670,25 +670,25 @@ static pic_value
 pic_pair_for_each(pic_state *pic)
 {
   struct pic_proc *proc;
-  size_t argc;
+  size_t argc, i;
   pic_value *args;
-  int i;
-  pic_value cars;
+  pic_value arg;
 
   pic_get_args(pic, "l*", &proc, &argc, &args);
 
   do {
-    cars = pic_nil_value();
-    for (i = argc - 1; i >= 0; --i) {
+    arg = pic_nil_value();
+    for (i = 0; i < argc; ++i) {
       if (! pic_pair_p(args[i])) {
         break;
       }
-      cars = pic_cons(pic, pic_car(pic, args[i]), cars);
+      pic_push(pic, pic_car(pic, args[i]), arg);
       args[i] = pic_cdr(pic, args[i]);
     }
-    if (i >= 0)
+    if (i != argc) {
       break;
-    pic_apply(pic, proc, cars);
+    }
+    pic_apply(pic, proc, pic_reverse(pic, arg));
   } while (1);
 
   return pic_none_value();
diff --git a/port.c b/port.c
index 5cbcb1b8..ec61d984 100644
--- a/port.c
+++ b/port.c
@@ -521,20 +521,15 @@ pic_port_read_blob(pic_state *pic)
 {
   struct pic_port *port = pic_stdin(pic);
   pic_blob *blob;
-  int k;
-  size_t i;
+  size_t k, i;
 
-  pic_get_args(pic, "i|p", &k, &port);
+  pic_get_args(pic, "k|p", &k, &port);
 
   assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, PIC_PORT_OPEN, "read-bytevector");
 
-  if (k < 0) {
-    pic_errorf(pic, "read-bytevector: index must be non-negative %d", k);
-  }
+  blob = pic_make_blob(pic, k);
 
-  blob = pic_make_blob(pic, (size_t)k);
-
-  i = xfread(blob->data, sizeof(char), (size_t)k, port->file);
+  i = xfread(blob->data, sizeof(char), k, port->file);
   if (i == 0) {
     return pic_eof_object();
   }
@@ -550,27 +545,27 @@ pic_port_read_blob_ip(pic_state *pic)
 {
   struct pic_port *port;
   struct pic_blob *bv;
-  int n, start, end;
+  int n;
   char *buf;
-  size_t i, len;
+  size_t start, end, i, len;
 
-  n = pic_get_args(pic, "b|pii", &bv, &port, &start, &end);
+  n = pic_get_args(pic, "b|pkk", &bv, &port, &start, &end);
   switch (n) {
   case 1:
     port = pic_stdin(pic);
   case 2:
     start = 0;
   case 3:
-    end = (int)bv->len;
+    end = bv->len;
   }
 
   assert_port_profile(port, PIC_PORT_IN | PIC_PORT_BINARY, PIC_PORT_OPEN, "read-bytevector!");
 
-  if (end - start < 0) {
+  if (end < start) {
     pic_errorf(pic, "read-bytevector!: end index must be greater than or equal to start index");
   }
 
-  len = (size_t)(end - start);
+  len = end - start;
 
   buf = pic_calloc(pic, len, sizeof(char));
   i = xfread(buf, sizeof(char), len, port->file);
@@ -581,7 +576,7 @@ pic_port_read_blob_ip(pic_state *pic)
     return pic_eof_object();
   }
   else {
-    return pic_int_value((int)i);
+    return pic_size_value(i);
   }
 }
 
@@ -656,16 +651,17 @@ pic_port_write_blob(pic_state *pic)
 {
   struct pic_blob *blob;
   struct pic_port *port;
-  int start, end, n, i;
+  int n;
+  size_t start, end, i;
 
-  n = pic_get_args(pic, "b|pii", &blob, &port, &start, &end);
+  n = pic_get_args(pic, "b|pkk", &blob, &port, &start, &end);
   switch (n) {
   case 1:
     port = pic_stdout(pic);
   case 2:
     start = 0;
   case 3:
-    end = (int)blob->len;
+    end = blob->len;
   }
 
   assert_port_profile(port, PIC_PORT_OUT | PIC_PORT_BINARY, PIC_PORT_OPEN, "write-bytevector");
diff --git a/read.c b/read.c
index 7deb5eb2..be160c0d 100644
--- a/read.c
+++ b/read.c
@@ -209,7 +209,7 @@ read_symbol(pic_state *pic, struct pic_port *port, const char *str)
 
   for (i = 0; i < len; ++i) {
     if (pic->reader->typecase == PIC_CASE_FOLD) {
-      buf[i] = tolower(str[i]);
+      buf[i] = (char)tolower(str[i]);
     } else {
       buf[i] = str[i];
     }
@@ -222,7 +222,7 @@ read_symbol(pic_state *pic, struct pic_port *port, const char *str)
     }
     len += 1;
     buf = pic_realloc(pic, buf, len + 1);
-    buf[len - 1] = c;
+    buf[len - 1] = (char)c;
   }
 
   sym = pic_intern(pic, buf, len);
@@ -240,9 +240,9 @@ read_uinteger(pic_state *pic, struct pic_port *port, int c, char buf[])
     read_error(pic, "expected one or more digits");
   }
 
-  buf[i++] = c;
+  buf[i++] = (char)c;
   while (isdigit(c = peek(port))) {
-    buf[i++] = next(port);
+    buf[i++] = (char)next(port);
   }
 
   buf[i] = '\0';
@@ -262,12 +262,12 @@ read_suffix(pic_state *pic, struct pic_port *port, char buf[])
     return i;
   }
 
-  buf[i++] = next(port);
+  buf[i++] = (char)next(port);
 
   switch ((c = next(port))) {
   case '-':
   case '+':
-    buf[i++] = c;
+    buf[i++] = (char)c;
     c = next(port);
   default:
     return i + read_uinteger(pic, port, c, buf + i);
@@ -284,14 +284,14 @@ read_unsigned(pic_state *pic, struct pic_port *port, int c)
 
   switch (peek(port)) {
   case '.':
-    buf[i++] = next(port);
+    buf[i++] = (char)next(port);
     i += read_uinteger(pic, port, next(port), buf + i);
     read_suffix(pic, port, buf + i);
     return pic_float_value(atof(buf));
 
   default:
     read_suffix(pic, port, buf + i);
-    return pic_int_value((int)atof(buf));
+    return pic_int_value((int)(atof(buf)));
   }
 }
 
@@ -404,7 +404,7 @@ read_char(pic_state *pic, struct pic_port *port, const char *str)
     }
   }
 
-  return pic_char_value(c);
+  return pic_char_value((char)c);
 
  fail:
   read_error(pic, "unexpected character while reading character literal");
@@ -436,7 +436,7 @@ read_string(pic_state *pic, struct pic_port *port, const char *name)
       case 'r': c = '\r'; break;
       }
     }
-    buf[cnt++] = c;
+    buf[cnt++] = (char)c;
     if (cnt >= size) {
       buf = pic_realloc(pic, buf, size *= 2);
     }
@@ -474,15 +474,15 @@ read_pipe(pic_state *pic, struct pic_port *port, const char *str)
       case 'r': c = '\r'; break;
       case 'x':
         i = 0;
-        while ((HEX_BUF[i++] = next(port)) != ';') {
+        while ((HEX_BUF[i++] = (char)next(port)) != ';') {
           if (i >= sizeof HEX_BUF)
             read_error(pic, "expected ';'");
         }
-        c = strtol(HEX_BUF, NULL, 16);
+        c = (char)strtol(HEX_BUF, NULL, 16);
         break;
       }
     }
-    buf[cnt++] = c;
+    buf[cnt++] = (char)c;
     if (cnt >= size) {
       buf = pic_realloc(pic, buf, size *= 2);
     }
@@ -500,7 +500,8 @@ read_blob(pic_state *pic, struct pic_port *port, const char *str)
 {
   int nbits, n, c;
   size_t len, i;
-  char *dat, buf[256];
+  char buf[256];
+  unsigned char *dat;
   pic_blob *blob;
 
   UNUSED(str);
@@ -530,7 +531,7 @@ read_blob(pic_state *pic, struct pic_port *port, const char *str)
     }
     len += 1;
     dat = pic_realloc(pic, dat, len);
-    dat[len - 1] = n;
+    dat[len - 1] = (unsigned char)n;
     c = next(port);
   }
 
@@ -710,7 +711,7 @@ read_nullable(pic_state *pic, struct pic_port *port, int c)
     read_error(pic, "invalid character at the seeker head");
   }
 
-  buf[i++] = c;
+  buf[i++] = (char)c;
 
   while (i < sizeof buf) {
     trie = trie->table[c];
@@ -721,7 +722,7 @@ read_nullable(pic_state *pic, struct pic_port *port, int c)
     if (trie->table[c] == NULL) {
       break;
     }
-    buf[i++] = next(port);
+    buf[i++] = (char)next(port);
   }
   if (i == sizeof buf) {
     read_error(pic, "too long dispatch string");
diff --git a/string.c b/string.c
index b53055f4..f9f15a59 100644
--- a/string.c
+++ b/string.c
@@ -233,22 +233,21 @@ pic_str_string_p(pic_state *pic)
 static pic_value
 pic_str_string(pic_state *pic)
 {
-  size_t argc;
+  size_t argc, i;
   pic_value *argv;
   pic_str *str;
   char *buf;
-  size_t i;
 
   pic_get_args(pic, "*", &argc, &argv);
 
-  buf = pic_alloc(pic, argc);
+  buf = pic_alloc(pic, (size_t)argc);
 
   for (i = 0; i < argc; ++i) {
     pic_assert_type(pic, argv[i], char);
     buf[i] = pic_char(argv[i]);
   }
 
-  str = pic_make_str(pic, buf, argc);
+  str = pic_make_str(pic, buf, (size_t)argc);
   pic_free(pic, buf);
 
   return pic_obj_value(str);
@@ -257,10 +256,10 @@ pic_str_string(pic_state *pic)
 static pic_value
 pic_str_make_string(pic_state *pic)
 {
-  int len;
+  size_t len;
   char c = ' ';
 
-  pic_get_args(pic, "i|c", &len, &c);
+  pic_get_args(pic, "k|c", &len, &c);
 
   return pic_obj_value(pic_make_str_fill(pic, len, c));
 }
@@ -272,16 +271,16 @@ pic_str_string_length(pic_state *pic)
 
   pic_get_args(pic, "s", &str);
 
-  return pic_int_value(pic_strlen(str));
+  return pic_size_value(pic_strlen(str));
 }
 
 static pic_value
 pic_str_string_ref(pic_state *pic)
 {
   pic_str *str;
-  int k;
+  size_t k;
 
-  pic_get_args(pic, "si", &str, &k);
+  pic_get_args(pic, "sk", &str, &k);
 
   return pic_char_value(pic_str_ref(pic, str, k));
 }
@@ -290,9 +289,8 @@ pic_str_string_ref(pic_state *pic)
   static pic_value                                                      \
   pic_str_string_##name(pic_state *pic)                                 \
   {                                                                     \
-    size_t argc;                                                        \
+    size_t argc, i;                                                     \
     pic_value *argv;                                                    \
-    size_t i;                                                           \
                                                                         \
     pic_get_args(pic, "*", &argc, &argv);                               \
                                                                         \
@@ -321,9 +319,10 @@ static pic_value
 pic_str_string_copy(pic_state *pic)
 {
   pic_str *str;
-  int n, start, end;
+  int n;
+  size_t start, end;
 
-  n = pic_get_args(pic, "s|ii", &str, &start, &end);
+  n = pic_get_args(pic, "s|kk", &str, &start, &end);
 
   switch (n) {
   case 1:
@@ -358,8 +357,8 @@ static pic_value
 pic_str_string_map(pic_state *pic)
 {
   struct pic_proc *proc;
-  size_t argc, i, len, j;
   pic_value *argv, vals, val;
+  size_t argc, i, len, j;
 
   pic_get_args(pic, "l*", &proc, &argc, &argv);
 
@@ -396,7 +395,7 @@ static pic_value
 pic_str_string_for_each(pic_state *pic)
 {
   struct pic_proc *proc;
-  size_t argc, i, len, j;
+  size_t argc, len, i, j;
   pic_value *argv, vals, val;
 
   pic_get_args(pic, "l*", &proc, &argc, &argv);
@@ -429,7 +428,7 @@ pic_str_list_to_string(pic_state *pic)
 {
   pic_str *str;
   pic_value list, e;
-  int i = 0;
+  size_t i = 0;
 
   pic_get_args(pic, "o", &list);
 
@@ -455,9 +454,10 @@ pic_str_string_to_list(pic_state *pic)
 {
   pic_str *str;
   pic_value list;
-  int n, start, end, i;
+  int n;
+  size_t start, end, i;
 
-  n = pic_get_args(pic, "s|ii", &str, &start, &end);
+  n = pic_get_args(pic, "s|kk", &str, &start, &end);
 
   switch (n) {
   case 1:
diff --git a/symbol.c b/symbol.c
index 0cbbf78a..115582c8 100644
--- a/symbol.c
+++ b/symbol.c
@@ -80,7 +80,7 @@ pic_ungensym(pic_state *pic, pic_sym base)
   if ((occr = strrchr(name, '@')) == NULL) {
     pic_panic(pic, "logic flaw");
   }
-  return pic_intern(pic, name, occr - name);
+  return pic_intern(pic, name, (size_t)(occr - name));
 }
 
 bool
diff --git a/system.c b/system.c
index 4c54b905..1b251661 100644
--- a/system.c
+++ b/system.c
@@ -105,7 +105,7 @@ pic_system_getenvs(pic_state *pic)
 
   for (envp = pic->envp; *envp; ++envp) {
     pic_str *key, *val;
-    int i;
+    size_t i;
 
     for (i = 0; (*envp)[i] != '='; ++i)
       ;
diff --git a/time.c b/time.c
index a0a1ffb6..83716db8 100644
--- a/time.c
+++ b/time.c
@@ -27,7 +27,7 @@ pic_current_jiffy(pic_state *pic)
   pic_get_args(pic, "");
 
   c = clock();
-  return pic_int_value((int)c);
+  return pic_int_value((int)c); /* The year 2038 problem :-| */
 }
 
 static pic_value
diff --git a/vector.c b/vector.c
index 2a3099f7..33070d24 100644
--- a/vector.c
+++ b/vector.c
@@ -26,7 +26,7 @@ struct pic_vector *
 pic_make_vec_from_list(pic_state *pic, pic_value data)
 {
   struct pic_vector *vec;
-  size_t i, len;
+  size_t len, i;
 
   len = pic_length(pic, data);
 
@@ -51,14 +51,13 @@ pic_vec_vector_p(pic_state *pic)
 static pic_value
 pic_vec_vector(pic_state *pic)
 {
-  size_t argc;
+  size_t argc, i;
   pic_value *argv;
   pic_vec *vec;
-  size_t i;
 
   pic_get_args(pic, "*", &argc, &argv);
 
-  vec = pic_make_vec(pic, argc);
+  vec = pic_make_vec(pic, (size_t)argc);
 
   for (i = 0; i < argc; ++i) {
     vec->data[i] = argv[i];
@@ -71,15 +70,15 @@ static pic_value
 pic_vec_make_vector(pic_state *pic)
 {
   pic_value v;
-  int n, k;
-  size_t i;
+  int n;
+  size_t k, i;
   struct pic_vector *vec;
 
-  n = pic_get_args(pic, "i|o", &k, &v);
+  n = pic_get_args(pic, "k|o", &k, &v);
 
   vec = pic_make_vec(pic, k);
   if (n == 2) {
-    for (i = 0; i < (size_t)k; ++i) {
+    for (i = 0; i < k; ++i) {
       vec->data[i] = v;
     }
   }
@@ -93,18 +92,18 @@ pic_vec_vector_length(pic_state *pic)
 
   pic_get_args(pic, "v", &v);
 
-  return pic_int_value(v->len);
+  return pic_size_value(v->len);
 }
 
 static pic_value
 pic_vec_vector_ref(pic_state *pic)
 {
   struct pic_vector *v;
-  int k;
+  size_t k;
 
-  pic_get_args(pic, "vi", &v, &k);
+  pic_get_args(pic, "vk", &v, &k);
 
-  if (k < 0 || v->len <= (size_t)k) {
+  if (v->len <= k) {
     pic_errorf(pic, "vector-ref: index out of range");
   }
   return v->data[k];
@@ -114,12 +113,12 @@ static pic_value
 pic_vec_vector_set(pic_state *pic)
 {
   struct pic_vector *v;
-  int k;
+  size_t k;
   pic_value o;
 
-  pic_get_args(pic, "vio", &v, &k, &o);
+  pic_get_args(pic, "vko", &v, &k, &o);
 
-  if (k < 0 || v->len <= (size_t)k) {
+  if (v->len <= k) {
     pic_errorf(pic, "vector-set!: index out of range");
   }
   v->data[k] = o;
@@ -130,9 +129,10 @@ static pic_value
 pic_vec_vector_copy_i(pic_state *pic)
 {
   pic_vec *to, *from;
-  int n, at, start, end;
+  int n;
+  size_t at, start, end;
 
-  n = pic_get_args(pic, "viv|ii", &to, &at, &from, &start, &end);
+  n = pic_get_args(pic, "vkv|kk", &to, &at, &from, &start, &end);
 
   switch (n) {
   case 3:
@@ -161,9 +161,10 @@ static pic_value
 pic_vec_vector_copy(pic_state *pic)
 {
   pic_vec *vec, *to;
-  int n, start, end, i = 0;
+  int n;
+  size_t start, end, i = 0;
 
-  n = pic_get_args(pic, "v|ii", &vec, &start, &end);
+  n = pic_get_args(pic, "v|kk", &vec, &start, &end);
 
   switch (n) {
   case 1:
@@ -172,6 +173,10 @@ pic_vec_vector_copy(pic_state *pic)
     end = vec->len;
   }
 
+  if (end < start) {
+    pic_errorf(pic, "vector-copy: end index must not be less than start index");
+  }
+
   to = pic_make_vec(pic, end - start);
   while (start < end) {
     to->data[i++] = vec->data[start++];
@@ -183,8 +188,8 @@ pic_vec_vector_copy(pic_state *pic)
 static pic_value
 pic_vec_vector_append(pic_state *pic)
 {
-  size_t argc, i, j, len;
   pic_value *argv;
+  size_t argc, i, j, len;
   pic_vec *vec;
 
   pic_get_args(pic, "*", &argc, &argv);
@@ -213,9 +218,10 @@ pic_vec_vector_fill_i(pic_state *pic)
 {
   pic_vec *vec;
   pic_value obj;
-  int n, start, end;
+  int n;
+  size_t start, end;
 
-  n = pic_get_args(pic, "vo|ii", &vec, &obj, &start, &end);
+  n = pic_get_args(pic, "vo|kk", &vec, &obj, &start, &end);
 
   switch (n) {
   case 2:
@@ -241,7 +247,7 @@ pic_vec_vector_map(pic_state *pic)
 
   pic_get_args(pic, "l*", &proc, &argc, &argv);
 
-  len = SIZE_MAX;
+  len = INT_MAX;
   for (i = 0; i < argc; ++i) {
     pic_assert_type(pic, argv[i], vec);
 
@@ -272,7 +278,7 @@ pic_vec_vector_for_each(pic_state *pic)
 
   pic_get_args(pic, "l*", &proc, &argc, &argv);
 
-  len = SIZE_MAX;
+  len = INT_MAX;
   for (i = 0; i < argc; ++i) {
     pic_assert_type(pic, argv[i], vec);
 
@@ -315,9 +321,10 @@ pic_vec_vector_to_list(pic_state *pic)
 {
   struct pic_vector *vec;
   pic_value list;
-  int n, start, end, i;
+  int n;
+  size_t start, end, i;
 
-  n = pic_get_args(pic, "v|ii", &vec, &start, &end);
+  n = pic_get_args(pic, "v|kk", &vec, &start, &end);
 
   switch (n) {
   case 1:
@@ -339,10 +346,11 @@ pic_vec_vector_to_string(pic_state *pic)
 {
   pic_vec *vec;
   char *buf;
-  int n, start, end, i;
+  int n;
+  size_t start, end, i;
   pic_str *str;
 
-  n = pic_get_args(pic, "v|ii", &vec, &start, &end);
+  n = pic_get_args(pic, "v|kk", &vec, &start, &end);
 
   switch (n) {
   case 1:
@@ -351,6 +359,10 @@ pic_vec_vector_to_string(pic_state *pic)
     end = vec->len;
   }
 
+  if (end < start) {
+    pic_errorf(pic, "vector->string: end index must not be less than start index");
+  }
+
   buf = pic_alloc(pic, end - start);
 
   for (i = start; i < end; ++i) {
@@ -369,10 +381,12 @@ static pic_value
 pic_vec_string_to_vector(pic_state *pic)
 {
   pic_str *str;
-  int n, start, end, i;
+  int n;
+  size_t start, end;
+  size_t i;
   pic_vec *vec;
 
-  n = pic_get_args(pic, "s|ii", &str, &start, &end);
+  n = pic_get_args(pic, "s|kk", &str, &start, &end);
 
   switch (n) {
   case 1:
@@ -381,10 +395,14 @@ pic_vec_string_to_vector(pic_state *pic)
     end = pic_strlen(str);
   }
 
+  if (end < start) {
+    pic_errorf(pic, "string->vector: end index must not be less than start index");
+  }
+
   vec = pic_make_vec(pic, end - start);
 
-  for (i = start; i < end; ++i) {
-    vec->data[i - start] = pic_char_value(pic_str_ref(pic, str, i));
+  for (i = 0; i < end - start; ++i) {
+    vec->data[i] = pic_char_value(pic_str_ref(pic, str, i + start));
   }
   return pic_obj_value(vec);
 }
diff --git a/vm.c b/vm.c
index 92af1ce7..accb47ce 100644
--- a/vm.c
+++ b/vm.c
@@ -35,26 +35,27 @@ pic_get_proc(pic_state *pic)
 }
 
 /**
- * char type
- * ---- ----
- *  o   object
- *  i   int
- *  I   int with exactness
- *  f   float
- *  F   float with exactness
- *  s   string object
- *  z   c string
- *  m   symbol
- *  v   vector object
- *  b   bytevector object
- *  c   char
- *  l   lambda object
- *  p   port object
- *  d   dictionary object
- *  e   error object
+ * char type                 desc.
+ * ---- ----                 ----
+ *  o   pic_value *          object
+ *  i   int *                int
+ *  I   int *, bool *        int with exactness
+ *  k   size_t *             size_t implicitly converted from int
+ *  f   double *             float
+ *  F   double *, bool *     float with exactness
+ *  s   pic_str **           string object
+ *  z   char **              c string
+ *  m   pic_sym *            symbol
+ *  v   pic_vec **           vector object
+ *  b   pic_blob **          bytevector object
+ *  c   char *               char
+ *  l   struct pic_proc **   lambda object
+ *  p   struct pic_port **   port object
+ *  d   struct pic_dict **   dictionary object
+ *  e   struct pic_error **  error object
  *
- *  |  optional operator
- *  *  variable length operator
+ *  |                        optional operator
+ *  *   int *, pic_value **  variable length operator
  */
 
 int
@@ -196,6 +197,35 @@ pic_get_args(pic_state *pic, const char *format, ...)
       }
       break;
     }
+    case 'k': {
+      size_t *k;
+
+      k = va_arg(ap, size_t *);
+      if (i < argc) {
+        pic_value v;
+        int x;
+
+        v = GET_OPERAND(pic, i);
+        switch (pic_type(v)) {
+        case PIC_TT_INT:
+          x = pic_int(v);
+          if (x < 0) {
+            pic_errorf(pic, "pic_get_args: expected non-negative int, but got ~s", v);
+          }
+          if (sizeof(unsigned) > sizeof(size_t)) {
+            if ((unsigned)x > (unsigned)SIZE_MAX) {
+              pic_errorf(pic, "pic_get_args: int unrepresentable with size_t ~s", v);
+            }
+          }
+          *k = (size_t)x;
+          break;
+        default:
+          pic_errorf(pic, "pic_get_args: expected int, but got ~s", v);
+        }
+        i++;
+      }
+      break;
+    }
     case 's': {
       pic_str **str;
       pic_value v;
@@ -280,14 +310,14 @@ pic_get_args(pic_state *pic, const char *format, ...)
       break;
     }
     case 'c': {
-      char *c;
+      char *k;
       pic_value v;
 
-      c = va_arg(ap, char *);
+      k = va_arg(ap, char *);
       if (i < argc) {
         v = GET_OPERAND(pic,i);
         if (pic_char_p(v)) {
-          *c = pic_char(v);
+          *k = pic_char(v);
         }
         else {
           pic_errorf(pic, "pic_get_args: expected char, but got ~s", v);
@@ -392,7 +422,7 @@ pic_get_args(pic_state *pic, const char *format, ...)
     n = va_arg(ap, size_t *);
     argv = va_arg(ap, pic_value **);
     if (i <= argc) {
-      *n = argc - i;
+      *n = (size_t)(argc - i);
       *argv = &GET_OPERAND(pic, i);
       i = argc;
     }
@@ -488,7 +518,7 @@ vm_push_env(pic_state *pic)
 {
   pic_callinfo *ci = pic->ci;
 
-  ci->env = (struct pic_env *)pic_obj_alloc(pic, offsetof(struct pic_env, storage) + sizeof(pic_value) * ci->regc, PIC_TT_ENV);
+  ci->env = (struct pic_env *)pic_obj_alloc(pic, offsetof(struct pic_env, storage) + sizeof(pic_value) * (size_t)(ci->regc), PIC_TT_ENV);
   ci->env->up = ci->up;
   ci->env->regc = ci->regc;
   ci->env->regs = ci->regs;
@@ -581,7 +611,7 @@ pic_apply5(pic_state *pic, struct pic_proc *proc, pic_value arg1, pic_value arg2
 # define VM_LOOP_END } }
 #endif
 
-#define PUSH(v) ((pic->sp >= pic->stend) ? abort() : (*pic->sp++ = (v)))
+#define PUSH(v) (*pic->sp++ = (v))
 #define POP() (*--pic->sp)
 
 #define PUSHCI() (++pic->ci)
@@ -650,11 +680,10 @@ pic_apply5(pic_state *pic, struct pic_proc *proc, pic_value arg1, pic_value arg2
 #endif
 
 pic_value
-pic_apply(pic_state *pic, struct pic_proc *proc, pic_value argv)
+pic_apply(pic_state *pic, struct pic_proc *proc, pic_value args)
 {
   pic_code c;
   size_t ai = pic_gc_arena_preserve(pic);
-  size_t argc, i;
   pic_code boot[2];
 
 #if PIC_DIRECT_THREADED_VM
@@ -674,26 +703,29 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value argv)
   pic_callinfo *cibase;
 #endif
 
-  if (! pic_list_p(argv)) {
+  if (! pic_list_p(args)) {
     pic_errorf(pic, "argv must be a proper list");
   }
+  else {
+    int argc, i;
 
-  argc = pic_length(pic, argv) + 1;
+    argc = (int)pic_length(pic, args) + 1;
 
-  VM_BOOT_PRINT;
+    VM_BOOT_PRINT;
 
-  PUSH(pic_obj_value(proc));
-  for (i = 1; i < argc; ++i) {
-    PUSH(pic_car(pic, argv));
-    argv = pic_cdr(pic, argv);
+    PUSH(pic_obj_value(proc));
+    for (i = 1; i < argc; ++i) {
+      PUSH(pic_car(pic, args));
+      args = pic_cdr(pic, args);
+    }
+
+    /* boot! */
+    boot[0].insn = OP_CALL;
+    boot[0].u.i = argc;
+    boot[1].insn = OP_STOP;
+    pic->ip = boot;
   }
 
-  /* boot! */
-  boot[0].insn = OP_CALL;
-  boot[0].u.i = argc;
-  boot[1].insn = OP_STOP;
-  pic->ip = boot;
-
   VM_LOOP {
     CASE(OP_NOP) {
       NEXT;
@@ -827,7 +859,6 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value argv)
     CASE(OP_CALL) {
       pic_value x, v;
       pic_callinfo *ci;
-      struct pic_proc *proc;
 
       if (c.u.i == -1) {
         pic->sp += pic->ci[1].retc - 1;
@@ -843,6 +874,10 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value argv)
 
       VM_CALL_PRINT;
 
+      if (pic->sp >= pic->stend) {
+        pic_panic(pic, "VM stack overflow");
+      }
+
       ci = PUSHCI();
       ci->argc = c.u.i;
       ci->retc = 1;
@@ -954,7 +989,6 @@ pic_apply(pic_state *pic, struct pic_proc *proc, pic_value argv)
     CASE(OP_LAMBDA) {
       pic_value self;
       struct pic_irep *irep;
-      struct pic_proc *proc;
 
       self = pic->ci->fp[0];
       if (! pic_proc_p(self)) {
@@ -1090,7 +1124,7 @@ pic_value
 pic_apply_trampoline(pic_state *pic, struct pic_proc *proc, pic_value args)
 {
   static const pic_code iseq[2] = {
-    { OP_NOP, {} },
+    { OP_NOP, { .i = 0 } },
     { OP_TAILCALL, { .i = -1 } }
   };
 
@@ -1107,7 +1141,7 @@ pic_apply_trampoline(pic_state *pic, struct pic_proc *proc, pic_value args)
   ci = PUSHCI();
   ci->ip = (pic_code *)iseq;
   ci->fp = pic->sp;
-  ci->retc = pic_length(pic, args);
+  ci->retc = (int)pic_length(pic, args);
 
   if (ci->retc == 0) {
     return pic_none_value();