diff --git a/extlib/benz/codegen.c b/extlib/benz/codegen.c
index 85f4c53f..cc9222d3 100644
--- a/extlib/benz/codegen.c
+++ b/extlib/benz/codegen.c
@@ -617,7 +617,7 @@ typedef struct codegen_context {
   size_t klen, kcapa;
   double *nums;
   size_t flen, fcapa;
-  pic_value *pool;
+  struct pic_object **pool;
   size_t plen, pcapa;
 
   struct codegen_context *up;
@@ -643,7 +643,7 @@ codegen_context_init(pic_state *pic, codegen_context *cxt, codegen_context *up,
   cxt->ilen = 0;
   cxt->icapa = PIC_IREP_SIZE;
 
-  cxt->pool = pic_calloc(pic, PIC_POOL_SIZE, sizeof(pic_value));
+  cxt->pool = pic_calloc(pic, PIC_POOL_SIZE, sizeof(struct pic_object *));
   cxt->plen = 0;
   cxt->pcapa = PIC_POOL_SIZE;
 
@@ -674,7 +674,7 @@ codegen_context_destroy(pic_state *pic, codegen_context *cxt)
   irep->u.s.irep = pic_realloc(pic, cxt->irep, sizeof(union irep_node) * cxt->ilen);
   irep->u.s.ints = pic_realloc(pic, cxt->ints, sizeof(int) * cxt->klen);
   irep->u.s.nums = pic_realloc(pic, cxt->nums, sizeof(double) * cxt->flen);
-  irep->pool = pic_realloc(pic, cxt->pool, sizeof(pic_value) * cxt->plen);
+  irep->pool = pic_realloc(pic, cxt->pool, sizeof(struct pic_object *) * cxt->plen);
   irep->ncode = cxt->clen;
   irep->nirep = cxt->ilen;
   irep->nints = cxt->klen;
@@ -698,7 +698,7 @@ codegen_context_destroy(pic_state *pic, codegen_context *cxt)
 
 #define check_code_size(pic, cxt) check_size(pic, cxt, c, code, pic_code)
 #define check_irep_size(pic, cxt) check_size(pic, cxt, i, irep, struct pic_irep *)
-#define check_pool_size(pic, cxt) check_size(pic, cxt, p, pool, pic_value)
+#define check_pool_size(pic, cxt) check_size(pic, cxt, p, pool, struct pic_object *)
 #define check_ints_size(pic, cxt) check_size(pic, cxt, k, ints, int)
 #define check_nums_size(pic, cxt) check_size(pic, cxt, f, nums, double)
 
@@ -770,7 +770,7 @@ index_global(pic_state *pic, codegen_context *cxt, pic_sym *name)
 
   check_pool_size(pic, cxt);
   pidx = (int)cxt->plen++;
-  cxt->pool[pidx] = pic_obj_value(slot);
+  cxt->pool[pidx] = (struct pic_object *)(slot);
 
   return pidx;
 }
@@ -975,9 +975,10 @@ codegen_quote(pic_state *pic, codegen_context *cxt, pic_value obj, bool tailpos)
     emit_i(pic, cxt, OP_PUSHCHAR, pidx);
     break;
   default:
+    assert(pic_obj_p(obj));
     check_pool_size(pic, cxt);
     pidx = (int)cxt->plen++;
-    cxt->pool[pidx] = obj;
+    cxt->pool[pidx] = pic_obj_ptr(obj);
     emit_i(pic, cxt, OP_PUSHCONST, pidx);
     break;
   }
diff --git a/extlib/benz/gc.c b/extlib/benz/gc.c
index 0b7d4507..3114f772 100644
--- a/extlib/benz/gc.c
+++ b/extlib/benz/gc.c
@@ -466,7 +466,7 @@ gc_mark_phase(pic_state *pic)
   for (list = pic->ireps.next; list != &pic->ireps; list = list->next) {
     struct pic_irep *irep = (struct pic_irep *)list;
     for (j = 0; j < irep->npool; ++j) {
-      gc_mark(pic, irep->pool[j]);
+      gc_mark_object(pic, irep->pool[j]);
     }
   }
 
diff --git a/extlib/benz/include/picrin/irep.h b/extlib/benz/include/picrin/irep.h
index c01ac2b9..7804c2d4 100644
--- a/extlib/benz/include/picrin/irep.h
+++ b/extlib/benz/include/picrin/irep.h
@@ -41,7 +41,7 @@ struct pic_irep {
       } *irep;
     } s;
   } u;
-  pic_value *pool;              /* pool of heap objects */
+  struct pic_object **pool;     /* pool of heap objects */
   size_t ncode, nirep, nints, nnums, npool;
 };
 
diff --git a/extlib/benz/vm.c b/extlib/benz/vm.c
index 7cbfa2be..a75d9fa9 100644
--- a/extlib/benz/vm.c
+++ b/extlib/benz/vm.c
@@ -424,15 +424,15 @@ pic_apply(pic_state *pic, struct pic_proc *proc, int argc, pic_value *argv)
       NEXT;
     }
     CASE(OP_PUSHCONST) {
-      PUSH(pic->ci->irep->pool[c.a]);
+      PUSH(pic_obj_value(pic->ci->irep->pool[c.a]));
       NEXT;
     }
     CASE(OP_GREF) {
-      PUSH(vm_gref(pic, pic_box_ptr(pic->ci->irep->pool[c.a]), NULL)); /* FIXME */
+      PUSH(vm_gref(pic, (struct pic_box *)(pic->ci->irep->pool[c.a]), NULL)); /* FIXME */
       NEXT;
     }
     CASE(OP_GSET) {
-      vm_gset(pic_box_ptr(pic->ci->irep->pool[c.a]), POP());
+      vm_gset((struct pic_box *)(pic->ci->irep->pool[c.a]), POP());
       PUSH(pic_undef_value());
       NEXT;
     }