diff --git a/extlib/xhash b/extlib/xhash
index ddc2ea28..0b5f935a 160000
--- a/extlib/xhash
+++ b/extlib/xhash
@@ -1 +1 @@
-Subproject commit ddc2ea288b37b3f5de37024ff2648d11aa18811a
+Subproject commit 0b5f935aa7a236f1ef1787f81dce7f5ba679e95b
diff --git a/include/picrin/value.h b/include/picrin/value.h
index 023902a3..4161b403 100644
--- a/include/picrin/value.h
+++ b/include/picrin/value.h
@@ -13,7 +13,7 @@ extern "C" {
  * pic_sym is just an alias to unsigned int.
  */
 
-typedef unsigned pic_sym;
+typedef int pic_sym;
 
 /**
  * `undef` values never seen from user-end: that is,
diff --git a/src/bool.c b/src/bool.c
index 74018c63..8f8c75f1 100644
--- a/src/bool.c
+++ b/src/bool.c
@@ -42,10 +42,10 @@ internal_equal_p(pic_state *pic, pic_value x, pic_value y, size_t depth, xhash *
       pic_errorf(pic, "Stack overflow in equal\n");
     }
     if (pic_pair_p(x) || pic_vec_p(x)) {
-      if (xh_get(ht, pic_obj_ptr(x)) != NULL) {
+      if (xh_get_ptr(ht, pic_obj_ptr(x)) != NULL) {
         return true;            /* `x' was seen already.  */
       } else {
-        xh_put(ht, pic_obj_ptr(x), NULL);
+        xh_put_ptr(ht, pic_obj_ptr(x), NULL);
       }
     }
   }
diff --git a/src/symbol.c b/src/symbol.c
index 2ea530d5..10fd3822 100644
--- a/src/symbol.c
+++ b/src/symbol.c
@@ -20,13 +20,13 @@ pic_intern(pic_state *pic, const char *str, size_t len)
   cstr[len] = '\0';
   memcpy(cstr, str, len);
 
-  e = xh_get(&pic->syms, cstr);
+  e = xh_get_str(&pic->syms, cstr);
   if (e) {
     return xh_val(e, pic_sym);
   }
 
   id = pic->sym_cnt++;
-  xh_put(&pic->syms, cstr, &id);
+  xh_put_str(&pic->syms, cstr, &id);
   xh_put_int(&pic->sym_names, id, &cstr);
   return id;
 }
diff --git a/src/write.c b/src/write.c
index 4122e600..bd13ac44 100644
--- a/src/write.c
+++ b/src/write.c
@@ -84,14 +84,14 @@ traverse_shared(struct writer_control *p, pic_value obj)
   switch (pic_type(obj)) {
   case PIC_TT_PAIR:
   case PIC_TT_VECTOR:
-    e = xh_get(&p->labels, pic_obj_ptr(obj));
+    e = xh_get_ptr(&p->labels, pic_obj_ptr(obj));
     if (e == NULL) {
       c = -1;
-      xh_put(&p->labels, pic_obj_ptr(obj), &c);
+      xh_put_ptr(&p->labels, pic_obj_ptr(obj), &c);
     }
     else if (xh_val(e, int) == -1) {
       c = p->cnt++;
-      xh_put(&p->labels, pic_obj_ptr(obj), &c);
+      xh_put_ptr(&p->labels, pic_obj_ptr(obj), &c);
       break;
     }
     else {
@@ -130,17 +130,17 @@ write_pair(struct writer_control *p, struct pic_pair *pair)
   else if (pic_pair_p(pair->cdr)) {
 
     /* shared objects */
-    if ((e = xh_get(&p->labels, pic_obj_ptr(pair->cdr))) && xh_val(e, int) != -1) {
+    if ((e = xh_get_ptr(&p->labels, pic_obj_ptr(pair->cdr))) && xh_val(e, int) != -1) {
       xfprintf(p->file, " . ");
 
-      if ((xh_get(&p->visited, pic_obj_ptr(pair->cdr)))) {
+      if ((xh_get_ptr(&p->visited, pic_obj_ptr(pair->cdr)))) {
         xfprintf(p->file, "#%d#", xh_val(e, int));
         return;
       }
       else {
         xfprintf(p->file, "#%d=", xh_val(e, int));
         c = 1;
-        xh_put(&p->visited, pic_obj_ptr(pair->cdr), &c);
+        xh_put_ptr(&p->visited, pic_obj_ptr(pair->cdr), &c);
       }
     }
     else {
@@ -184,16 +184,16 @@ write_core(struct writer_control *p, pic_value obj)
 
   /* shared objects */
   if (pic_vtype(obj) == PIC_VTYPE_HEAP
-      && (e = xh_get(&p->labels, pic_obj_ptr(obj)))
+      && (e = xh_get_ptr(&p->labels, pic_obj_ptr(obj)))
       && xh_val(e, int) != -1) {
-    if ((xh_get(&p->visited, pic_obj_ptr(obj)))) {
+    if ((xh_get_ptr(&p->visited, pic_obj_ptr(obj)))) {
       xfprintf(file, "#%d#", xh_val(e, int));
       return;
     }
     else {
       xfprintf(file, "#%d=", xh_val(e, int));
       c = 1;
-      xh_put(&p->visited, pic_obj_ptr(obj), &c);
+      xh_put_ptr(&p->visited, pic_obj_ptr(obj), &c);
     }
   }