diff --git a/app_dart/lib/src/service/scheduler.dart b/app_dart/lib/src/service/scheduler.dart
index ca1ef72..c9b0080 100644
--- a/app_dart/lib/src/service/scheduler.dart
+++ b/app_dart/lib/src/service/scheduler.dart
@@ -472,7 +472,7 @@
         } else {
           try {
             final RepositorySlug slug = checkRunEvent.repository!.slug();
-            final String gitBranch = checkRunEvent.checkRun!.checkSuite!.headBranch!;
+            final String gitBranch = checkRunEvent.checkRun!.checkSuite!.headBranch ?? Config.defaultBranch(slug);
             final String sha = checkRunEvent.checkRun!.headSha!;
 
             // Only merged commits are added to the datastore. If a matching commit is found, this must be a postsubmit checkrun.