diff --git a/codex-rs/codex-mcp/src/runtime.rs b/codex-rs/codex-mcp/src/runtime.rs
index ad607df754..fb6ccea9ec 100644
--- a/codex-rs/codex-mcp/src/runtime.rs
+++ b/codex-rs/codex-mcp/src/runtime.rs
@@ -148,7 +148,7 @@ mod tests {
                 env_http_headers: None,
             },
             experimental_environment: experimental_environment.map(str::to_string),
-            ..stdio_server(None)
+            ..stdio_server(/*experimental_environment*/ None)
         }
     }