diff --git a/jerry-core/ecma/operations/ecma-container-object.c b/jerry-core/ecma/operations/ecma-container-object.c
index 0dadc5ce51..0732c02353 100644
--- a/jerry-core/ecma/operations/ecma-container-object.c
+++ b/jerry-core/ecma/operations/ecma-container-object.c
@@ -64,11 +64,14 @@ ecma_op_internal_buffer_append (ecma_collection_t *container_p, /**< internal co
 {
   JERRY_ASSERT (container_p != NULL);
 
-  ecma_collection_push_back (container_p, ecma_copy_value_if_not_object (key_arg));
-
   if (lit_id == LIT_MAGIC_STRING_WEAKMAP_UL || lit_id == LIT_MAGIC_STRING_MAP_UL)
   {
-    ecma_collection_push_back (container_p, ecma_copy_value_if_not_object (value_arg));
+    ecma_value_t values[] = { ecma_copy_value_if_not_object (key_arg), ecma_copy_value_if_not_object (value_arg) };
+    ecma_collection_append (container_p, values, 2);
+  }
+  else
+  {
+    ecma_collection_push_back (container_p, ecma_copy_value_if_not_object (key_arg));
   }
 
   ECMA_CONTAINER_SET_SIZE (container_p, ECMA_CONTAINER_GET_SIZE (container_p) + 1);