diff --git a/extlib/xhash b/extlib/xhash
index b9d10d4f..44c9f36d 160000
--- a/extlib/xhash
+++ b/extlib/xhash
@@ -1 +1 @@
-Subproject commit b9d10d4fc9bed39c95f0155f520ea1a8b37d70fe
+Subproject commit 44c9f36dca1bbc2b158c812359a7e9d5a5f7e9bb
diff --git a/include/picrin.h b/include/picrin.h
index 6cd0182c..060327a1 100644
--- a/include/picrin.h
+++ b/include/picrin.h
@@ -33,6 +33,8 @@ extern "C" {
 #include <setjmp.h>
 #include <stdio.h>
 
+#include "xhash/xhash.h"
+
 #if __STDC_VERSION__ >= 201112L
 # define NORETURN _Noreturn
 #elif __GNUC__ || __clang__
@@ -94,12 +96,12 @@ typedef struct {
   pic_sym sADD, sSUB, sMUL, sDIV, sMINUS;
   pic_sym sEQ, sLT, sLE, sGT, sGE, sNOT;
 
-  struct xhash *sym_tbl;
+  xhash *sym_tbl;
   const char **sym_pool;
   size_t slen, scapa;
   int uniq_sym_count;
 
-  struct xhash *global_tbl;
+  xhash *global_tbl;
   pic_value *globals;
   size_t glen, gcapa;
 
diff --git a/include/picrin/lib.h b/include/picrin/lib.h
index 3d85cf1a..85812788 100644
--- a/include/picrin/lib.h
+++ b/include/picrin/lib.h
@@ -13,7 +13,7 @@ struct pic_lib {
   PIC_OBJECT_HEADER
   pic_value name;
   struct pic_senv *senv;
-  struct xhash *exports;
+  xhash *exports;
 };
 
 #define pic_lib_ptr(o) ((struct pic_lib *)pic_ptr(o))
diff --git a/include/picrin/macro.h b/include/picrin/macro.h
index b02ebf11..3b2f4ab9 100644
--- a/include/picrin/macro.h
+++ b/include/picrin/macro.h
@@ -13,7 +13,7 @@ struct pic_senv {
   PIC_OBJECT_HEADER
   struct pic_senv *up;
   /* positive for variables, negative for macros (bitwise-not) */
-  struct xhash *tbl;
+  xhash *tbl;
   struct pic_syntax **stx;
   size_t xlen, xcapa;
 };
diff --git a/src/codegen.c b/src/codegen.c
index 588b4f56..7e36dcb6 100644
--- a/src/codegen.c
+++ b/src/codegen.c
@@ -11,7 +11,6 @@
 #include "picrin/proc.h"
 #include "picrin/lib.h"
 #include "picrin/macro.h"
-#include "xhash/xhash.h"
 
 #if PIC_NONE_IS_FALSE
 # define OP_PUSHNONE OP_PUSHFALSE
@@ -80,7 +79,7 @@ typedef struct analyze_scope {
   bool varg;
   int argc, localc;
   /* if variable v is captured, then xh_get(var_tbl, v) == 1 */
-  struct xhash *var_tbl;
+  xhash *var_tbl;
   pic_sym *vars;
 
   struct analyze_scope *up;
@@ -103,8 +102,8 @@ static void pop_scope(analyze_state *);
   } while (0)
 
 #define register_renamed_symbol(pic, state, slot, lib, name) do {       \
-    struct xh_entry *e;                                                 \
-    if (! (e = xh_get(lib->senv->tbl, name)))                           \
+    xh_entry *e;                                                 \
+    if (! (e = xh_get_int(lib->senv->tbl, pic_intern_cstr(pic, name)))) \
       pic_error(pic, "internal error! native VM procedure not found");  \
     state->slot = e->val;                                               \
   } while (0)
@@ -113,8 +112,8 @@ static analyze_state *
 new_analyze_state(pic_state *pic)
 {
   analyze_state *state;
-  struct xhash *global_tbl;
-  struct xh_iter it;
+  xhash *global_tbl;
+  xh_iter it;
   struct pic_lib *stdlib;
 
   state = (analyze_state *)pic_alloc(pic, sizeof(analyze_state));
@@ -149,7 +148,7 @@ new_analyze_state(pic_state *pic)
 
   global_tbl = pic->global_tbl;
   for (xh_begin(global_tbl, &it); ! xh_isend(&it); xh_next(&it)) {
-    xh_put(state->scope->var_tbl, it.e->key, 0);
+    xh_put_int(state->scope->var_tbl, (long)it.e->key, 0);
   }
 
   return state;
@@ -171,7 +170,7 @@ push_scope(analyze_state *state, pic_value args)
 
   scope = (analyze_scope *)pic_alloc(pic, sizeof(analyze_scope));
   scope->up = state->scope;
-  scope->var_tbl = xh_new();
+  scope->var_tbl = xh_new_int();
   scope->varg = false;
   scope->vars = analyze_args(pic, args, &scope->varg, &scope->argc, &scope->localc);
 
@@ -180,7 +179,7 @@ push_scope(analyze_state *state, pic_value args)
   }
 
   for (i = 1; i < scope->argc + scope->localc; ++i) {
-    xh_put(scope->var_tbl, pic_symbol_name(pic, scope->vars[i]), 0);
+    xh_put_int(scope->var_tbl, scope->vars[i], 0);
   }
 
   state->scope = scope;
@@ -204,16 +203,15 @@ static int
 lookup_var(analyze_state *state, pic_sym sym)
 {
   analyze_scope *scope = state->scope;
-  struct xh_entry *e;
+  xh_entry *e;
   int depth = 0;
-  const char *key = pic_symbol_name(state->pic, sym);
 
  enter:
 
-  e = xh_get(scope->var_tbl, key);
+  e = xh_get_int(scope->var_tbl, sym);
   if (e) {
     if (depth > 0) {            /* mark dirty */
-      xh_put(scope->var_tbl, key, 1);
+      xh_put_int(scope->var_tbl, sym, 1);
     }
     return depth;
   }
@@ -230,9 +228,14 @@ define_var(analyze_state *state, pic_sym sym)
 {
   pic_state *pic = state->pic;
   analyze_scope *scope = state->scope;
-  const char *name = pic_symbol_name(pic, sym);
+  xh_entry *e;
 
-  xh_put(state->scope->var_tbl, name, 0);
+  if ((e = xh_get_int(scope->var_tbl, sym))) {
+    pic_warn(pic, "redefining variable");
+    return;
+  }
+
+  xh_put_int(scope->var_tbl, sym, 0);
 
   scope->localc++;
   scope->vars = (pic_sym *)pic_realloc(pic, scope->vars, sizeof(pic_sym) * (scope->argc + scope->localc));
@@ -638,7 +641,7 @@ analyze_lambda(analyze_state *state, pic_value obj)
     closes = pic_nil_value();
     for (i = 1; i < scope->argc + scope->localc; ++i) {
       pic_sym var = scope->vars[i];
-      if (xh_get(scope->var_tbl, pic_symbol_name(pic, var))->val == 1) {
+      if (xh_get_int(scope->var_tbl, var)->val == 1) {
         closes = pic_cons(pic, pic_symbol_value(var), closes);
       }
     }
@@ -669,7 +672,7 @@ typedef struct resolver_scope {
   int depth;
   bool varg;
   int argc, localc;
-  struct xhash *cvs, *lvs;
+  xhash *cvs, *lvs;
   unsigned cv_num;
 
   struct resolver_scope *up;
@@ -721,26 +724,26 @@ push_resolver_scope(resolver_state *state, pic_value args, pic_value locals, boo
   scope = (resolver_scope *)pic_alloc(pic, sizeof(resolver_scope));
   scope->up = state->scope;
   scope->depth = scope->up ? scope->up->depth + 1 : 0;
-  scope->lvs = xh_new();
-  scope->cvs = xh_new();
+  scope->lvs = xh_new_int();
+  scope->cvs = xh_new_int();
   scope->argc = pic_length(pic, args) + 1;
   scope->localc = pic_length(pic, locals);
   scope->varg = varg;
 
   /* arguments */
   for (i = 1; i < scope->argc; ++i) {
-    xh_put(scope->lvs, pic_symbol_name(pic, pic_sym(pic_list_ref(pic, args, i - 1))), i);
+    xh_put_int(scope->lvs, pic_sym(pic_list_ref(pic, args, i - 1)), i);
   }
 
   /* locals */
   for (i = 0; i < scope->localc; ++i) {
-    xh_put(scope->lvs, pic_symbol_name(pic, pic_sym(pic_list_ref(pic, locals, i))), scope->argc + i);
+    xh_put_int(scope->lvs, pic_sym(pic_list_ref(pic, locals, i)), scope->argc + i);
   }
 
   /* closed variables */
   scope->cv_num = 0;
   for (i = 0, c = pic_length(pic, closes); i < c; ++i) {
-    xh_put(scope->cvs, pic_symbol_name(pic, pic_sym(pic_list_ref(pic, closes, i))), scope->cv_num++);
+    xh_put_int(scope->cvs, pic_sym(pic_list_ref(pic, closes, i)), scope->cv_num++);
   }
 
   state->scope = scope;
@@ -763,18 +766,17 @@ pop_resolver_scope(resolver_state *state)
 static bool
 is_closed(resolver_state *state, pic_sym sym)
 {
-  return xh_get(state->scope->cvs, pic_symbol_name(state->pic, sym)) != NULL;
+  return xh_get_int(state->scope->cvs, sym) != NULL;
 }
 
 static pic_value
 resolve_gref(resolver_state *state, pic_sym sym)
 {
   pic_state *pic = state->pic;
-  const char *name = pic_symbol_name(pic, sym);
-  struct xh_entry *e;
+  xh_entry *e;
   size_t i;
 
-  if ((e = xh_get(pic->global_tbl, name))) {
+  if ((e = xh_get_int(pic->global_tbl, sym))) {
     i = e->val;
   }
   else {
@@ -782,7 +784,7 @@ resolve_gref(resolver_state *state, pic_sym sym)
     if (i >= pic->gcapa) {
       pic_error(pic, "global table overflow");
     }
-    xh_put(pic->global_tbl, name, i);
+    xh_put_int(pic->global_tbl, sym, i);
   }
   return pic_list(pic, 2, pic_symbol_value(state->sGREF), pic_int_value(i));
 }
@@ -793,7 +795,7 @@ resolve_lref(resolver_state *state, pic_sym sym)
   pic_state *pic = state->pic;
   int i;
 
-  i = xh_get(state->scope->lvs, pic_symbol_name(pic, sym))->val;
+  i = xh_get_int(state->scope->lvs, sym)->val;
 
   return pic_list(pic, 2, pic_symbol_value(state->sLREF), pic_int_value(i));
 }
@@ -810,7 +812,7 @@ resolve_cref(resolver_state *state, int depth, pic_sym sym)
     scope = scope->up;
   }
 
-  i = xh_get(scope->cvs, pic_symbol_name(pic, sym))->val;
+  i = xh_get_int(scope->cvs, sym)->val;
 
   return pic_list(pic, 3,
                   pic_symbol_value(state->sCREF),
@@ -984,7 +986,7 @@ push_codegen_context(codegen_state *state, pic_value args, pic_value locals, boo
   pic_state *pic = state->pic;
   codegen_context *cxt;
   int i, c;
-  struct xhash *vars;
+  xhash *vars;
 
   cxt = (codegen_context *)pic_alloc(pic, sizeof(codegen_context));
   cxt->up = state->cxt;
@@ -993,12 +995,12 @@ push_codegen_context(codegen_state *state, pic_value args, pic_value locals, boo
   cxt->varg = varg;
 
   /* number local variables */
-  vars = xh_new();
+  vars = xh_new_int();
   for (i = 1; i < cxt->argc; ++i) {
-    xh_put(vars, pic_symbol_name(pic, pic_sym(pic_list_ref(pic, args, i - 1))), i);
+    xh_put_int(vars, pic_sym(pic_list_ref(pic, args, i - 1)), i);
   }
   for (i = 0; i < cxt->localc; ++i) {
-    xh_put(vars, pic_symbol_name(pic, pic_sym(pic_list_ref(pic, locals, i))), cxt->argc + i);
+    xh_put_int(vars, pic_sym(pic_list_ref(pic, locals, i)), cxt->argc + i);
   }
 
   /* closed variables */
@@ -1007,7 +1009,7 @@ push_codegen_context(codegen_state *state, pic_value args, pic_value locals, boo
   for (i = 0, c = pic_length(pic, closes); i < c; ++i) {
     i = cxt->cv_num++;
     cxt->cv_tbl = (unsigned *)pic_realloc(pic, cxt->cv_tbl, sizeof(unsigned) * cxt->cv_num);
-    cxt->cv_tbl[i] = xh_get(vars, pic_symbol_name(pic, pic_sym(pic_list_ref(pic, closes, i))))->val;
+    cxt->cv_tbl[i] = xh_get_int(vars, pic_sym(pic_list_ref(pic, closes, i)))->val;
   }
 
   xh_destroy(vars);
@@ -1439,61 +1441,68 @@ pic_compile(pic_state *pic, pic_value obj)
 }
 
 static int
-scope_global_define(pic_state *pic, const char *name)
+global_ref(pic_state *pic, const char *name)
 {
-  struct xh_entry *e;
+  xh_entry *e;
+  pic_sym sym;
 
-  if ((e = xh_get(pic->global_tbl, name))) {
-    pic_warn(pic, "redefining global");
-    return e->val;
+  sym = pic_intern_cstr(pic, name);
+  if (! (e = xh_get_int(pic->lib->senv->tbl, sym))) {
+    return -1;
   }
-  e = xh_put(pic->global_tbl, name, pic->glen++);
+  assert(e->val >= 0);
+  if (! (e = xh_get_int(pic->global_tbl, e->val))) {
+    return -1;
+  }
+  return e->val;
+}
+
+static int
+global_def(pic_state *pic, const char *name)
+{
+  pic_sym sym, gsym;
+  size_t gidx;
+
+  sym = pic_intern_cstr(pic, name);
+  if ((gidx = global_ref(pic, name)) != -1) {
+    pic_warn(pic, "redefining global");
+    return gidx;
+  }
+
+  gsym = pic_gensym(pic, sym);
+
+  /* register to the senv */
+  xh_put_int(pic->lib->senv->tbl, sym, gsym);
+
+  /* register to the global table */
+  gidx = pic->glen++;
   if (pic->glen >= pic->gcapa) {
     pic_error(pic, "global table overflow");
   }
-  return e->val;
+  xh_put_int(pic->global_tbl, gsym, gidx);
+
+  return gidx;
 }
 
 void
 pic_define(pic_state *pic, const char *name, pic_value val)
 {
-  int idx;
-  pic_sym gsym;
-
-  gsym = pic_gensym(pic, pic_intern_cstr(pic, name));
-
   /* push to the global arena */
-  idx = scope_global_define(pic, pic_symbol_name(pic, gsym));
-  pic->globals[idx] = val;
-
-  /* register to the senv */
-  xh_put(pic->lib->senv->tbl, name, gsym);
+  pic->globals[global_def(pic, name)] = val;
 
   /* export! */
   pic_export(pic, pic_intern_cstr(pic, name));
 }
 
-static int
-global_ref(pic_state *pic, const char *name)
-{
-  struct xh_entry *e;
-
-  if (! (e = xh_get(pic->lib->senv->tbl, name))) {
-    pic_error(pic, "symbol not defined");
-  }
-  assert(e->val >= 0);
-  if (! (e = xh_get(pic->global_tbl, pic_symbol_name(pic, (pic_sym)e->val)))) {
-    pic_abort(pic, "logic flaw");
-  }
-  return e->val;
-}
-
 pic_value
 pic_ref(pic_state *pic, const char *name)
 {
   int gid;
 
   gid = global_ref(pic, name);
+  if (gid == -1) {
+    pic_error(pic, "symbol not defined");
+  }
   return pic->globals[gid];
 }
 
@@ -1503,6 +1512,9 @@ pic_set(pic_state *pic, const char *name, pic_value value)
   int gid;
 
   gid = global_ref(pic, name);
+  if (gid == -1) {
+    pic_error(pic, "symbol not defined");
+  }
   pic->globals[gid] = value;
 }
 
diff --git a/src/gc.c b/src/gc.c
index bab5505f..8bdd10e0 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -15,7 +15,6 @@
 #include "picrin/macro.h"
 #include "picrin/lib.h"
 #include "picrin/var.h"
-#include "xhash/xhash.h"
 
 #if GC_DEBUG
 # include <string.h>
diff --git a/src/init.c b/src/init.c
index de8c2bb6..c2b9fdf6 100644
--- a/src/init.c
+++ b/src/init.c
@@ -9,7 +9,6 @@
 #include "picrin/pair.h"
 #include "picrin/lib.h"
 #include "picrin/macro.h"
-#include "xhash/xhash.h"
 
 void pic_init_bool(pic_state *);
 void pic_init_pair(pic_state *);
diff --git a/src/lib.c b/src/lib.c
index 683b42bc..90e5419a 100644
--- a/src/lib.c
+++ b/src/lib.c
@@ -6,7 +6,6 @@
 #include "picrin/lib.h"
 #include "picrin/pair.h"
 #include "picrin/macro.h"
-#include "xhash/xhash.h"
 
 struct pic_lib *
 pic_make_library(pic_state *pic, pic_value name)
@@ -29,7 +28,7 @@ pic_make_library(pic_state *pic, pic_value name)
 
   lib = (struct pic_lib *)pic_obj_alloc(pic, sizeof(struct pic_lib), PIC_TT_LIB);
   lib->senv = senv;
-  lib->exports = xh_new();
+  lib->exports = xh_new_int();
   lib->name = name;
 
   /* register! */
diff --git a/src/macro.c b/src/macro.c
index 2d2c3e85..3865d702 100644
--- a/src/macro.c
+++ b/src/macro.c
@@ -11,7 +11,6 @@
 #include "picrin/proc.h"
 #include "picrin/macro.h"
 #include "picrin/lib.h"
-#include "xhash/xhash.h"
 
 static pic_value macroexpand(pic_state *, pic_value, struct pic_senv *);
 static pic_value macroexpand_list(pic_state *, pic_value, struct pic_senv *);
@@ -23,7 +22,7 @@ pic_null_syntactic_env(pic_state *pic)
 
   senv = (struct pic_senv *)pic_obj_alloc(pic, sizeof(struct pic_senv), PIC_TT_SENV);
   senv->up = NULL;
-  senv->tbl = xh_new();
+  senv->tbl = xh_new_int();
   senv->stx = (struct pic_syntax **)pic_calloc(pic, PIC_MACROS_SIZE, sizeof(struct pic_syntax *));
   senv->xlen = 0;
   senv->xcapa = PIC_MACROS_SIZE;
@@ -32,8 +31,9 @@ pic_null_syntactic_env(pic_state *pic)
 }
 
 #define register_core_syntax(pic,senv,kind,name) do {			\
-    senv->stx[senv->xlen] = pic_syntax_new(pic, kind, pic_intern_cstr(pic, name)); \
-    xh_put(senv->tbl, name, ~senv->xlen);				\
+    pic_sym sym = pic_intern_cstr(pic, name);                           \
+    senv->stx[senv->xlen] = pic_syntax_new(pic, kind, sym);             \
+    xh_put_int(senv->tbl, sym, ~senv->xlen);				\
     senv->xlen++;							\
   } while (0)
 
@@ -83,7 +83,7 @@ new_local_senv(pic_state *pic, pic_value formals, struct pic_senv *up)
 
   senv = (struct pic_senv *)pic_obj_alloc(pic, sizeof(struct pic_senv), PIC_TT_SENV);
   senv->up = up;
-  senv->tbl = xh_new();
+  senv->tbl = xh_new_int();
   senv->stx = NULL;
   senv->xlen = 0;
   senv->xcapa = 0;
@@ -98,14 +98,14 @@ new_local_senv(pic_state *pic, pic_value formals, struct pic_senv *up)
       pic_error(pic, "syntax error");
     }
     sym = pic_sym(v);
-    xh_put(senv->tbl, pic_symbol_name(pic, sym), (int)pic_gensym(pic, sym));
+    xh_put_int(senv->tbl, sym, pic_gensym(pic, sym));
   }
   if (! pic_sym_p(a)) {
     a = macroexpand(pic, a, up);
   }
   if (pic_sym_p(a)) {
     sym = pic_sym(a);
-    xh_put(senv->tbl, pic_symbol_name(pic, sym), (int)pic_gensym(pic, sym));
+    xh_put_int(senv->tbl, sym, pic_gensym(pic, sym));
   }
   else if (! pic_nil_p(a)) {
     pic_error(pic, "syntax error");
@@ -180,7 +180,7 @@ void
 pic_import(pic_state *pic, pic_value spec)
 {
   struct pic_lib *lib;
-  struct xh_iter it;
+  xh_iter it;
 
   lib = pic_find_library(pic, spec);
   if (! lib) {
@@ -189,14 +189,14 @@ pic_import(pic_state *pic, pic_value spec)
   for (xh_begin(lib->exports, &it); ! xh_isend(&it); xh_next(&it)) {
 #if DEBUG
     if (it.e->val >= 0) {
-      printf("* importing %s as %s\n", it.e->key, pic_symbol_name(pic, (pic_sym)it.e->val));
+      printf("* importing %s as %s\n", pic_symbol_name(pic, (long)it.e->key), pic_symbol_name(pic, it.e->val));
     }
     else {
-      printf("* importing %s\n", it.e->key);
+      printf("* importing %s\n", pic_symbol_name(pic, (long)it.e->key));
     }
 #endif
     if (it.e->val >= 0) {
-      xh_put(pic->lib->senv->tbl, it.e->key, it.e->val);
+      xh_put_int(pic->lib->senv->tbl, (long)it.e->key, it.e->val);
     }
     else {                /* syntax object */
       size_t idx;
@@ -208,7 +208,7 @@ pic_import(pic_state *pic, pic_value spec)
       }
       /* bring macro object from imported lib */
       senv->stx[idx] = lib->senv->stx[~it.e->val];
-      xh_put(senv->tbl, it.e->key, ~idx);
+      xh_put_int(senv->tbl, (long)it.e->key, ~idx);
       senv->xlen++;
     }
   }
@@ -217,30 +217,32 @@ pic_import(pic_state *pic, pic_value spec)
 void
 pic_export(pic_state *pic, pic_sym sym)
 {
-  struct xh_entry *e;
+  xh_entry *e;
 
-  e = xh_get(pic->lib->senv->tbl, pic_symbol_name(pic, sym));
+  e = xh_get_int(pic->lib->senv->tbl, sym);
   if (! e) {
     pic_error(pic, "symbol not defined");
   }
-  xh_put(pic->lib->exports, e->key, e->val);
+  xh_put_int(pic->lib->exports, (long)e->key, e->val);
 }
 
 static void
 pic_defsyntax(pic_state *pic, const char *name, struct pic_proc *macro, struct pic_senv *mac_env)
 {
+  pic_sym sym;
   struct pic_syntax *stx;
   struct pic_senv *global_senv = pic->lib->senv;
   size_t idx;
 
-  stx = pic_syntax_new_macro(pic, pic_intern_cstr(pic, name), macro, mac_env);
+  sym = pic_intern_cstr(pic, name);
+  stx = pic_syntax_new_macro(pic, sym, macro, mac_env);
 
   idx = global_senv->xlen;
   if (idx >= global_senv->xcapa) {
     pic_abort(pic, "macro table overflow");
   }
   global_senv->stx[idx] = stx;
-  xh_put(global_senv->tbl, name, ~idx);
+  xh_put_int(global_senv->tbl, sym, ~idx);
   global_senv->xlen++;
 }
 
@@ -269,16 +271,16 @@ macroexpand(pic_state *pic, pic_value expr, struct pic_senv *senv)
     return macroexpand(pic, sc->expr, sc->senv);
   }
   case PIC_TT_SYMBOL: {
-    struct xh_entry *e;
+    xh_entry *e;
     pic_sym uniq;
 
     if (! pic_interned_p(pic, pic_sym(expr))) {
       return expr;
     }
     while (true) {
-      if ((e = xh_get(senv->tbl, pic_symbol_name(pic, pic_sym(expr)))) != NULL) {
+      if ((e = xh_get_int(senv->tbl, pic_sym(expr))) != NULL) {
 	if (e->val >= 0)
-	  return pic_symbol_value((pic_sym)e->val);
+	  return pic_symbol_value(e->val);
 	else
 	  return pic_obj_value(senv->stx[~e->val]);
       }
@@ -287,7 +289,7 @@ macroexpand(pic_state *pic, pic_value expr, struct pic_senv *senv)
       senv = senv->up;
     }
     uniq = pic_gensym(pic, pic_sym(expr));
-    xh_put(senv->tbl, pic_symbol_name(pic, pic_sym(expr)), (int)uniq);
+    xh_put_int(senv->tbl, pic_sym(expr), uniq);
     return pic_symbol_value(uniq);
   }
   case PIC_TT_PAIR: {
@@ -453,29 +455,28 @@ macroexpand(pic_state *pic, pic_value expr, struct pic_senv *senv)
 	return v;
       }
       case PIC_STX_DEFINE: {
-	pic_sym uniq;
-	pic_value var;
+	pic_sym var;
+	pic_value formals;
 
 	if (pic_length(pic, expr) < 2) {
 	  pic_error(pic, "syntax error");
 	}
 
-	var = pic_cadr(pic, expr);
-	if (pic_pair_p(var)) {
-	  struct pic_senv *in = new_local_senv(pic, pic_cdr(pic, var), senv);
+	formals = pic_cadr(pic, expr);
+	if (pic_pair_p(formals)) {
+	  struct pic_senv *in = new_local_senv(pic, pic_cdr(pic, formals), senv);
 	  pic_value a;
-	  pic_sym sym;
 
 	  /* defined symbol */
-	  a = pic_car(pic, var);
+	  a = pic_car(pic, formals);
           if (! pic_sym_p(a)) {
             a = macroexpand(pic, a, senv);
           }
 	  if (! pic_sym_p(a)) {
 	    pic_error(pic, "binding to non-symbol object");
 	  }
-	  sym = pic_sym(a);
-	  xh_put(senv->tbl, pic_symbol_name(pic, sym), (int)pic_gensym(pic, sym));
+	  var = pic_sym(a);
+	  xh_put_int(senv->tbl, var, pic_gensym(pic, var));
 
 	  /* binding value */
 	  v = pic_cons(pic, pic_symbol_value(pic_syntax(car)->sym),
@@ -488,14 +489,17 @@ macroexpand(pic_state *pic, pic_value expr, struct pic_senv *senv)
 	  return v;
 	}
 
-        if (! pic_sym_p(var)) {
-          var = macroexpand(pic, var, senv);
+        if (! pic_sym_p(formals)) {
+          formals = macroexpand(pic, formals, senv);
         }
-	if (! pic_sym_p(var)) {
+	if (! pic_sym_p(formals)) {
 	  pic_error(pic, "binding to non-symbol object");
 	}
-	uniq = pic_gensym(pic, pic_sym(var));
-	xh_put(senv->tbl, pic_symbol_name(pic, pic_sym(var)), (int)uniq);
+        var = pic_sym(formals);
+        /* do not make duplicate variable slot */
+        if (xh_get_int(senv->tbl, var) == NULL) {
+          xh_put_int(senv->tbl, var, pic_gensym(pic, var));
+        }
       }
 	FALLTHROUGH;
       case PIC_STX_SET:
diff --git a/src/state.c b/src/state.c
index f1a78dc5..a431f0cb 100644
--- a/src/state.c
+++ b/src/state.c
@@ -9,7 +9,6 @@
 #include "picrin/proc.h"
 #include "picrin/macro.h"
 #include "picrin/cont.h"
-#include "xhash/xhash.h"
 
 void pic_init_core(pic_state *);
 
@@ -53,14 +52,14 @@ pic_open(int argc, char *argv[], char **envp)
   init_heap(pic->heap);
 
   /* symbol table */
-  pic->sym_tbl = xh_new();
+  pic->sym_tbl = xh_new_str();
   pic->sym_pool = (const char **)calloc(PIC_SYM_POOL_SIZE, sizeof(const char *));
   pic->slen = 0;
   pic->scapa = pic->slen + PIC_SYM_POOL_SIZE;
   pic->uniq_sym_count = 0;
 
   /* global variables */
-  pic->global_tbl = xh_new();
+  pic->global_tbl = xh_new_int();
   pic->globals = (pic_value *)calloc(PIC_GLOBALS_SIZE, sizeof(pic_value));
   pic->glen = 0;
   pic->gcapa = PIC_GLOBALS_SIZE;
diff --git a/src/symbol.c b/src/symbol.c
index 62057ab7..8cd1f62c 100644
--- a/src/symbol.c
+++ b/src/symbol.c
@@ -8,12 +8,11 @@
 #include <assert.h>
 
 #include "picrin.h"
-#include "xhash/xhash.h"
 
 pic_sym
 pic_intern_cstr(pic_state *pic, const char *str)
 {
-  struct xh_entry *e;
+  xh_entry *e;
   pic_sym id;
 
   e = xh_get(pic->sym_tbl, str);
@@ -21,6 +20,8 @@ pic_intern_cstr(pic_state *pic, const char *str)
     return e->val;
   }
 
+  str = pic_strdup(pic, str);
+
   if (pic->slen >= pic->scapa) {
 
 #if DEBUG
@@ -31,7 +32,7 @@ pic_intern_cstr(pic_state *pic, const char *str)
     pic->sym_pool = pic_realloc(pic, pic->sym_pool, sizeof(const char *) * pic->scapa);
   }
   id = pic->slen++;
-  pic->sym_pool[id] = pic_strdup(pic, str);
+  pic->sym_pool[id] = str;
   xh_put(pic->sym_tbl, str, id);
   return id;
 }