diff --git a/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/spi/v1/FakeSubscriberServiceImpl.java b/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/spi/v1/FakeSubscriberServiceImpl.java
index 29e7f8c3de46..e3098ea2e732 100644
--- a/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/spi/v1/FakeSubscriberServiceImpl.java
+++ b/google-cloud-pubsub/src/test/java/com/google/cloud/pubsub/spi/v1/FakeSubscriberServiceImpl.java
@@ -208,6 +208,7 @@ public void sendStreamingResponse(StreamingPullResponse pullResponse)
       throws InterruptedException {
     waitForRegistedSubscription();
     synchronized (openedStreams) {
+      waitForOpenedStreams(1);
       openedStreams.get(getAndAdvanceCurrentStream()).responseObserver.onNext(pullResponse);
     }
   }