diff --git a/src/index.ts b/src/index.ts
index ee67339..2bc1fe3 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -198,8 +198,8 @@ const generateRelaychainGenesisFile = (config: Config, path: string, output: str
         }
       });
     }
-    _.merge(runtime.runtime_genesis_config, config.relaychain.runtimeGenesisConfig);
-    _.merge(runtime, config.relaychain.overrides);
+    _.merge(runtime.runtime_genesis_config || runtime, config.relaychain.runtimeGenesisConfig);
+    _.merge(runtime.runtime_genesis_config || runtime, config.relaychain.overrides);
   }
 
   // genesis parachains