diff --git a/google/firestore/v1/write.proto b/google/firestore/v1/write.proto
index 4ed0f5475f65b..90db49f52da92 100644
--- a/google/firestore/v1/write.proto
+++ b/google/firestore/v1/write.proto
@@ -264,6 +264,9 @@ message ExistenceFilter {
   //
   // If different from the count of documents in the client that match, the
   // client must manually determine which documents no longer match the target.
+  //
+  // The client can use the `unchanged_names` bloom filter to assist with
+  // this determination.
   int32 count = 2;
 
   // A bloom filter that contains the UTF-8 byte encodings of the resource names