diff --git a/google-cloud-clients/google-cloud-firestore/src/test/java/com/google/cloud/firestore/it/ITSystemTest.java b/google-cloud-clients/google-cloud-firestore/src/test/java/com/google/cloud/firestore/it/ITSystemTest.java
index 199219098475..de19f5492da7 100644
--- a/google-cloud-clients/google-cloud-firestore/src/test/java/com/google/cloud/firestore/it/ITSystemTest.java
+++ b/google-cloud-clients/google-cloud-firestore/src/test/java/com/google/cloud/firestore/it/ITSystemTest.java
@@ -920,6 +920,10 @@ public void queryWatch() throws Exception {
     //        case there is a hang during the test the whole suite isn't taken with it)
     //   D. After all updates have been performed and the expected number of events have been
     //      received, assertions on the events will be performed.
+    //
+    // Note: There is a potential that this test fails if the Firestore backend chooses not to send
+    // us individual changes for every document update, but rather merges two or more changes into
+    // a single event. We have, however, not seen any failures during thousands of test runs.
     ListenerRegistration registration = null;
     final ExecutorService updatesExecutor = Executors.newCachedThreadPool();