diff --git a/f8/utils.h b/f8/utils.h
index 6d03d4f..23c1c2b 100644
--- a/f8/utils.h
+++ b/f8/utils.h
@@ -33,43 +33,45 @@ namespace f8
                     abort();
                 }
                 void* p = (char*)obj + field.offset;
-                switch (field.type) {
-                case a8::reflect::ET_INT32:
-                    {
-                        *((int*)p) = reader.GetValue(field.field_name);
-                    }
-                    break;
-                case a8::reflect::ET_UINT32:
-                    {
-                        *((unsigned int*)p) = reader.GetValue(field.field_name);
-                    }
-                    break;
-                case a8::reflect::ET_INT64:
-                    {
-                        *((long long*)p) = reader.GetValue(field.field_name);
-                    }
-                    break;
-                case a8::reflect::ET_FLOAT:
-                    {
-                        *((float*)p) = reader.GetValue(field.field_name).GetDouble();
-                    }
-                    break;
-                case a8::reflect::ET_DOUBLE:
-                    {
-                        *((double*)p) = reader.GetValue(field.field_name);
-                    }
-                    break;
-                case a8::reflect::ET_STRING:
-                    {
-                        *((std::string*)p) = reader.GetValue(field.field_name).GetString();
-                    }
-                    break;
-                default:
-                    {
-                        abort();
+                if (reader.KeyExists(field.field_name)) {
+                    switch (field.type) {
+                    case a8::reflect::ET_INT32:
+                        {
+                            *((int*)p) = reader.GetValue(field.field_name);
+                        }
+                        break;
+                    case a8::reflect::ET_UINT32:
+                        {
+                            *((unsigned int*)p) = reader.GetValue(field.field_name);
+                        }
+                        break;
+                    case a8::reflect::ET_INT64:
+                        {
+                            *((long long*)p) = reader.GetValue(field.field_name);
+                        }
+                        break;
+                    case a8::reflect::ET_FLOAT:
+                        {
+                            *((float*)p) = reader.GetValue(field.field_name).GetDouble();
+                        }
+                        break;
+                    case a8::reflect::ET_DOUBLE:
+                        {
+                            *((double*)p) = reader.GetValue(field.field_name);
+                        }
+                        break;
+                    case a8::reflect::ET_STRING:
+                        {
+                            *((std::string*)p) = reader.GetValue(field.field_name).GetString();
+                        }
+                        break;
+                    default:
+                        {
+                            abort();
+                        }
                     }
+                    obj->__flags__.set(i);
                 }
-                obj->__flags__.set(i);
             }
             meta_list.push_back(obj);
         }