diff --git a/stage1/wasm.h b/stage1/wasm.h
index 276d340bbbd2941ae076e70e0775402316a2c33b..277f865563b7ac2eaee9b169f0556b5d12c0668a 100644
--- a/stage1/wasm.h
+++ b/stage1/wasm.h
@@ -52,6 +52,7 @@ static const char *WasmMut_toC(enum WasmMut val_type) {
         case WasmMut_var: return "";
         default: panic("unsupported mut");
     }
+    return NULL;
 }
 
 enum WasmOpcode {