diff --git a/cont.c b/cont.c
index 41a0fdb8..4e38e8c6 100644
--- a/cont.c
+++ b/cont.c
@@ -184,14 +184,14 @@ pic_values5(pic_state *pic, pic_value arg1, pic_value arg2, pic_value arg3, pic_
 }
 
 pic_value
-pic_values_by_array(pic_state *pic, int argc, pic_value *argv)
+pic_values_by_array(pic_state *pic, size_t argc, pic_value *argv)
 {
-  int i;
+  size_t i;
 
   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];
 }
@@ -211,15 +211,15 @@ pic_values_by_list(pic_state *pic, pic_value list)
   return pic_nil_p(list) ? pic_none_value() : pic->sp[0];
 }
 
-int
-pic_receive(pic_state *pic, int n, pic_value *argv)
+size_t
+pic_receive(pic_state *pic, size_t n, pic_value *argv)
 {
   pic_callinfo *ci;
-  int i, retc;
+  size_t i, retc;
 
   /* 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];
@@ -263,7 +263,7 @@ static pic_value
 pic_cont_call_with_values(pic_state *pic)
 {
   struct pic_proc *producer, *consumer;
-  int argc;
+  size_t argc;
   pic_value args[256];
 
   pic_get_args(pic, "ll", &producer, &consumer);
diff --git a/include/picrin/cont.h b/include/picrin/cont.h
index 01e86e11..645e6d9c 100644
--- a/include/picrin/cont.h
+++ b/include/picrin/cont.h
@@ -40,9 +40,9 @@ pic_value pic_values2(pic_state *, pic_value, pic_value);
 pic_value pic_values3(pic_state *, pic_value, pic_value, pic_value);
 pic_value pic_values4(pic_state *, pic_value, pic_value, pic_value, pic_value);
 pic_value pic_values5(pic_state *, pic_value, pic_value, pic_value, pic_value, pic_value);
-pic_value pic_values_by_array(pic_state *, int, pic_value *);
+pic_value pic_values_by_array(pic_state *, size_t, pic_value *);
 pic_value pic_values_by_list(pic_state *, pic_value);
-int pic_receive(pic_state *, int, pic_value *);
+size_t pic_receive(pic_state *, size_t, pic_value *);
 
 pic_value pic_escape(pic_state *, struct pic_proc *);
 
diff --git a/include/picrin/pair.h b/include/picrin/pair.h
index d6cf779d..d489b765 100644
--- a/include/picrin/pair.h
+++ b/include/picrin/pair.h
@@ -56,7 +56,7 @@ pic_value pic_list4(pic_state *, pic_value, pic_value, pic_value, pic_value);
 pic_value pic_list5(pic_state *, pic_value, pic_value, pic_value, pic_value, pic_value);
 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 *, int, pic_value *);
+pic_value pic_list_by_array(pic_state *, size_t, pic_value *);
 pic_value pic_make_list(pic_state *, size_t, pic_value);
 
 #define pic_for_each(var, list)                                 \
diff --git a/pair.c b/pair.c
index f2803f1a..b662534a 100644
--- a/pair.c
+++ b/pair.c
@@ -160,7 +160,7 @@ pic_list7(pic_state *pic, pic_value obj1, pic_value obj2, pic_value obj3, pic_va
 }
 
 pic_value
-pic_list_by_array(pic_state *pic, int c, pic_value *vs)
+pic_list_by_array(pic_state *pic, size_t c, pic_value *vs)
 {
   pic_value v;