diff --git a/extensions/xai/test-helpers.ts b/extensions/xai/test-helpers.ts
index 77848a1a8ac..637c4b7dc22 100644
--- a/extensions/xai/test-helpers.ts
+++ b/extensions/xai/test-helpers.ts
@@ -49,7 +49,7 @@ export function createXaiPayloadCaptureStream() {
   };
 }
 
-export function runXaiGrok4ResponseStream(streamFn: StreamFn | undefined) {
+export function runXaiGrok4ResponseStream(streamFn: StreamFn | null | undefined) {
   void streamFn?.(
     {
       api: "openai-responses",