diff --git a/Firestore/Source/Local/FSTMemoryPersistence.mm b/Firestore/Source/Local/FSTMemoryPersistence.mm
index f396ed8b84d..211c06e33f9 100644
--- a/Firestore/Source/Local/FSTMemoryPersistence.mm
+++ b/Firestore/Source/Local/FSTMemoryPersistence.mm
@@ -246,7 +246,7 @@ - (int)removeOrphanedDocumentsThroughSequenceNumber:(ListenSequenceNumber)upperB
   for (const auto &key : removed) {
     _sequenceNumbers.erase(key);
   }
-  return removed.size();
+  return (int)removed.size();
 }
 
 - (void)addReference:(const DocumentKey &)key {