diff --git a/include/picrin.h b/include/picrin.h
index ca043c09..b4036cb5 100644
--- a/include/picrin.h
+++ b/include/picrin.h
@@ -57,18 +57,11 @@ typedef struct {
   struct pic_env *up;
 } pic_callinfo;
 
-typedef struct pic_block {
-  struct pic_block *prev;
-  int depth;
-  struct pic_proc *in, *out;
-  unsigned refcnt;
-} pic_block;
-
 typedef struct {
   int argc;
   char **argv, **envp;
 
-  pic_block *blk;
+  struct pic_block *blk;
 
   pic_value *sp;
   pic_value *stbase, *stend;
diff --git a/include/picrin/cont.h b/include/picrin/cont.h
index b33b6755..0a0da9f1 100644
--- a/include/picrin/cont.h
+++ b/include/picrin/cont.h
@@ -9,11 +9,18 @@
 extern "C" {
 #endif
 
+struct pic_block {
+  PIC_OBJECT_HEADER
+  struct pic_block *prev;
+  int depth;
+  struct pic_proc *in, *out;
+};
+
 struct pic_cont {
   PIC_OBJECT_HEADER
   jmp_buf jmp;
 
-  pic_block *blk;
+  struct pic_block *blk;
 
   char *stk_pos, *stk_ptr;
   ptrdiff_t stk_len;
@@ -36,34 +43,6 @@ struct pic_cont {
   pic_value results;
 };
 
-#define PIC_BLK_INCREF(pic,blk) do {		\
-    (blk)->refcnt++;				\
-  } while (0)
-
-#define PIC_BLK_DECREF(pic,blk) do {			\
-    pic_block *_a = (blk), *_b;                         \
-    while (_a) {					\
-      if (! --_a->refcnt) {				\
-	_b = _a->prev;					\
-	pic_free((pic), _a);				\
-	_a = _b;					\
-      } else {						\
-	break;						\
-      }							\
-    }							\
-  } while (0)
-
-#define PIC_BLK_EXIT(pic) do {                           \
-    pic_block *_a;                                       \
-    while (pic->blk) {                                   \
-      if (pic->blk->out)                                 \
-        pic_apply0(pic, pic->blk->out);                  \
-      _a = pic->blk->prev;                               \
-      PIC_BLK_DECREF(pic, pic->blk);                     \
-      pic->blk = _a;                                     \
-    }                                                    \
-  } while (0)
-
 pic_value pic_values0(pic_state *);
 pic_value pic_values1(pic_state *, pic_value);
 pic_value pic_values2(pic_state *, pic_value, pic_value);
diff --git a/include/picrin/value.h b/include/picrin/value.h
index 283bac28..023902a3 100644
--- a/include/picrin/value.h
+++ b/include/picrin/value.h
@@ -115,7 +115,8 @@ enum pic_tt {
   PIC_TT_VAR,
   PIC_TT_IREP,
   PIC_TT_DATA,
-  PIC_TT_DICT
+  PIC_TT_DICT,
+  PIC_TT_BLK,
 };
 
 #define PIC_OBJECT_HEADER			\
@@ -268,6 +269,8 @@ pic_type_repr(enum pic_tt tt)
     return "data";
   case PIC_TT_DICT:
     return "dict";
+  case PIC_TT_BLK:
+    return "block";
   }
   UNREACHABLE();
 }
diff --git a/src/codegen.c b/src/codegen.c
index a5c35eb8..8f8d9aed 100644
--- a/src/codegen.c
+++ b/src/codegen.c
@@ -831,6 +831,7 @@ analyze_node(analyze_state *state, pic_value obj, bool tailpos)
   case PIC_TT_IREP:
   case PIC_TT_DATA:
   case PIC_TT_DICT:
+  case PIC_TT_BLK:
     pic_errorf(pic, "invalid expression given: ~s", obj);
   }
   UNREACHABLE();
diff --git a/src/cont.c b/src/cont.c
index bfda7310..30d26568 100644
--- a/src/cont.c
+++ b/src/cont.c
@@ -119,7 +119,6 @@ save_cont(pic_state *pic, struct pic_cont **c)
   cont = *c = (struct pic_cont *)pic_obj_alloc(pic, sizeof(struct pic_cont), PIC_TT_CONT);
 
   cont->blk = pic->blk;
-  PIC_BLK_INCREF(pic, cont->blk);
 
   cont->stk_len = native_stack_length(pic, &pos);
   cont->stk_pos = pos;
@@ -167,7 +166,7 @@ restore_cont(pic_state *pic, struct pic_cont *cont)
   void pic_vm_tear_off(pic_state *);
   char v;
   struct pic_cont *tmp = cont;
-  pic_block *blk;
+  struct pic_block *blk;
 
   pic_vm_tear_off(pic);         /* tear off */
 
@@ -180,8 +179,6 @@ restore_cont(pic_state *pic, struct pic_cont *cont)
 
   blk = pic->blk;
   pic->blk = cont->blk;
-  PIC_BLK_INCREF(pic, pic->blk);
-  PIC_BLK_DECREF(pic, blk);
 
   pic->stbase = (pic_value *)pic_realloc(pic, pic->stbase, sizeof(pic_value) * cont->st_len);
   memcpy(pic->stbase, cont->st_ptr, sizeof(pic_value) * cont->st_len);
@@ -211,7 +208,7 @@ restore_cont(pic_state *pic, struct pic_cont *cont)
 }
 
 static void
-walk_to_block(pic_state *pic, pic_block *here, pic_block *there)
+walk_to_block(pic_state *pic, struct pic_block *here, struct pic_block *there)
 {
   if (here == there)
     return;
@@ -229,7 +226,7 @@ walk_to_block(pic_state *pic, pic_block *here, pic_block *there)
 static pic_value
 pic_dynamic_wind(pic_state *pic, struct pic_proc *in, struct pic_proc *thunk, struct pic_proc *out)
 {
-  pic_block *here;
+  struct pic_block *here;
   pic_value val;
 
   if (in != NULL) {
@@ -237,17 +234,14 @@ pic_dynamic_wind(pic_state *pic, struct pic_proc *in, struct pic_proc *thunk, st
   }
 
   here = pic->blk;
-  pic->blk = (pic_block *)pic_alloc(pic, sizeof(pic_block));
+  pic->blk = (struct pic_block *)pic_obj_alloc(pic, sizeof(struct pic_block), PIC_TT_BLK);
   pic->blk->prev = here;
   pic->blk->depth = here->depth + 1;
   pic->blk->in = in;
   pic->blk->out = out;
-  pic->blk->refcnt = 1;
-  PIC_BLK_INCREF(pic, here);
 
   val = pic_apply0(pic, thunk);
 
-  PIC_BLK_DECREF(pic, pic->blk);
   pic->blk = here;
 
   if (out != NULL) {
diff --git a/src/gc.c b/src/gc.c
index 1ea3986e..4e3c82ff 100644
--- a/src/gc.c
+++ b/src/gc.c
@@ -322,18 +322,6 @@ gc_free(pic_state *pic, union header *bp)
 static void gc_mark(pic_state *, pic_value);
 static void gc_mark_object(pic_state *pic, struct pic_object *obj);
 
-static void
-gc_mark_block(pic_state *pic, pic_block *blk)
-{
-  while (blk) {
-    if (blk->in)
-      gc_mark_object(pic, (struct pic_object *)blk->in);
-    if (blk->out)
-      gc_mark_object(pic, (struct pic_object *)blk->out);
-    blk = blk->prev;
-  }
-}
-
 static bool
 gc_is_marked(union header *p)
 {
@@ -418,7 +406,7 @@ gc_mark_object(pic_state *pic, struct pic_object *obj)
     int i;
 
     /* block */
-    gc_mark_block(pic, cont->blk);
+    gc_mark_object(pic, (struct pic_object *)cont->blk);
 
     /* stack */
     for (stack = cont->st_ptr; stack != cont->st_ptr + cont->sp_offset; ++stack) {
@@ -506,6 +494,20 @@ gc_mark_object(pic_state *pic, struct pic_object *obj)
     }
     break;
   }
+  case PIC_TT_BLK: {
+    struct pic_block *blk = (struct pic_block *)obj;
+
+    if (blk->prev) {
+      gc_mark_object(pic, (struct pic_object *)blk->prev);
+    }
+    if (blk->in) {
+      gc_mark_object(pic, (struct pic_object *)blk->in);
+    }
+    if (blk->out) {
+      gc_mark_object(pic, (struct pic_object *)blk->out);
+    }
+    break;
+  }
   case PIC_TT_NIL:
   case PIC_TT_BOOL:
   case PIC_TT_FLOAT:
@@ -539,7 +541,9 @@ gc_mark_phase(pic_state *pic)
   xh_iter it;
 
   /* block */
-  gc_mark_block(pic, pic->blk);
+  if (pic->blk) {
+    gc_mark_object(pic, (struct pic_object *)pic->blk);
+  }
 
   /* stack */
   for (stack = pic->stbase; stack != pic->sp; ++stack) {
@@ -622,7 +626,6 @@ gc_finalize_object(pic_state *pic, struct pic_object *obj)
     pic_free(pic, cont->ci_ptr);
     pic_free(pic, cont->arena);
     pic_free(pic, cont->try_jmps);
-    PIC_BLK_DECREF(pic, cont->blk);
     break;
   }
   case PIC_TT_SENV: {
@@ -659,6 +662,9 @@ gc_finalize_object(pic_state *pic, struct pic_object *obj)
     xh_destroy(&dict->hash);
     break;
   }
+  case PIC_TT_BLK: {
+    break;
+  }
   case PIC_TT_NIL:
   case PIC_TT_BOOL:
   case PIC_TT_FLOAT:
diff --git a/src/macro.c b/src/macro.c
index 597eb57f..a31173de 100644
--- a/src/macro.c
+++ b/src/macro.c
@@ -416,6 +416,7 @@ macroexpand_node(pic_state *pic, pic_value expr, struct pic_senv *senv)
   case PIC_TT_IREP:
   case PIC_TT_DATA:
   case PIC_TT_DICT:
+  case PIC_TT_BLK:
     pic_errorf(pic, "unexpected value type: ~s", expr);
   }
   UNREACHABLE();
diff --git a/src/state.c b/src/state.c
index cdae3901..518d2ea4 100644
--- a/src/state.c
+++ b/src/state.c
@@ -23,18 +23,14 @@ pic_open(int argc, char *argv[], char **envp)
 
   pic = (pic_state *)malloc(sizeof(pic_state));
 
+  /* root block */
+  pic->blk = NULL;
+
   /* command line */
   pic->argc = argc;
   pic->argv = argv;
   pic->envp = envp;
 
-  /* root block */
-  pic->blk = (pic_block *)malloc(sizeof(pic_block));
-  pic->blk->prev = NULL;
-  pic->blk->depth = 0;
-  pic->blk->in = pic->blk->out = NULL;
-  pic->blk->refcnt = 1;
-
   /* prepare VM stack */
   pic->stbase = pic->sp = (pic_value *)calloc(PIC_STACK_SIZE, sizeof(pic_value));
   pic->stend = pic->stbase + PIC_STACK_SIZE;
@@ -135,6 +131,12 @@ pic_open(int argc, char *argv[], char **envp)
   register_renamed_symbol(pic, rEXPORT, "export");
   pic_gc_arena_restore(pic, ai);
 
+  /* root block */
+  pic->blk = (struct pic_block *)pic_obj_alloc(pic, sizeof(struct pic_block), PIC_TT_BLK);
+  pic->blk->prev = NULL;
+  pic->blk->depth = 0;
+  pic->blk->in = pic->blk->out = NULL;
+
   pic_init_core(pic);
 
   /* set library */
@@ -150,7 +152,12 @@ pic_close(pic_state *pic)
   xh_iter it;
 
   /* invoke exit handlers */
-  PIC_BLK_EXIT(pic);
+  while (pic->blk) {
+    if (pic->blk->out) {
+      pic_apply0(pic, pic->blk->out);
+    }
+    pic->blk = pic->blk->prev;
+  }
 
   /* clear out root objects */
   pic->sp = pic->stbase;
diff --git a/src/system.c b/src/system.c
index 73b27262..633d4a94 100644
--- a/src/system.c
+++ b/src/system.c
@@ -47,7 +47,7 @@ pic_system_exit(pic_state *pic)
     }
   }
 
-  PIC_BLK_EXIT(pic);
+  pic_close(pic);
 
   exit(status);
 }