diff --git a/jerry-core/vm/opcodes.c b/jerry-core/vm/opcodes.c
index b64620d63..73b29945e 100644
--- a/jerry-core/vm/opcodes.c
+++ b/jerry-core/vm/opcodes.c
@@ -252,7 +252,9 @@ opfunc_for_in (ecma_value_t left_value, /**< left value */
     *result_obj_p = ecma_make_object_value (obj_p);
   }
 
-  jmem_heap_free_block (prop_names_coll_p, sizeof (ecma_collection_header_t));
+  /* Note: We release the collection header here, and return the chunk list of the collection, which will
+   * be handled and released by the vm loop. */
+  jmem_pools_free (prop_names_coll_p, sizeof (ecma_collection_header_t));
   ecma_free_value (obj_expr_value);
 
   return prop_names_p;
diff --git a/jerry-core/vm/vm.c b/jerry-core/vm/vm.c
index 8bc2584a4..3e54f7a60 100644
--- a/jerry-core/vm/vm.c
+++ b/jerry-core/vm/vm.c
@@ -2816,6 +2816,7 @@ vm_loop (vm_frame_ctx_t *frame_ctx_p) /**< frame context */
 
           JERRY_ASSERT (!ecma_is_value_pointer (chunk_p->items[index]));
 
+          /* TODO: use collection iterator instead of directly accessing the collection chunks. */
           *stack_top_p++ = chunk_p->items[index];
           index++;