diff --git a/lib/util/git/parent-sha-cache.ts b/lib/util/git/parent-sha-cache.ts
index fef31e074bf3530cac82f209062c900b29371cc6..bec5e8253e93babb8cd08f91e6dcc9f7b2da1d47 100644
--- a/lib/util/git/parent-sha-cache.ts
+++ b/lib/util/git/parent-sha-cache.ts
@@ -7,7 +7,7 @@ export function getCachedBranchParentShaResult(
   const { branches } = getCache();
   const branch = branches?.find((branch) => branch.branchName === branchName);
 
-  if (branchSha === branch?.sha) {
+  if (branch?.parentSha && branchSha === branch?.sha) {
     return branch.parentSha;
   }