diff --git a/dev/tools/find_engine_commit.dart b/dev/tools/find_engine_commit.dart
index 8b87553..c8d67af 100644
--- a/dev/tools/find_engine_commit.dart
+++ b/dev/tools/find_engine_commit.dart
@@ -29,7 +29,7 @@
   _validate(args);
   await _fetchUpstream();
   await _fetchUpstream(engineRepo);
-  String flutterRevision;
+  String? flutterRevision;
   await for (final FlutterEngineRevision revision in _logEngineVersions()) {
     if (!await containsRevision(args[0], revision.engineRevision)) {
       if (flutterRevision == null) {