diff --git a/gradle/changelog/hg_default_branch.yaml b/gradle/changelog/hg_default_branch.yaml
new file mode 100644
index 0000000000..e62e933c6e
--- /dev/null
+++ b/gradle/changelog/hg_default_branch.yaml
@@ -0,0 +1,3 @@
+- type: fixed
+  description: Error in frontend without 'default' branch in hg repositories
+
diff --git a/scm-ui/ui-webapp/src/repos/sources/containers/Sources.tsx b/scm-ui/ui-webapp/src/repos/sources/containers/Sources.tsx
index 1bd3f30680..c87806d2e6 100644
--- a/scm-ui/ui-webapp/src/repos/sources/containers/Sources.tsx
+++ b/scm-ui/ui-webapp/src/repos/sources/containers/Sources.tsx
@@ -63,8 +63,10 @@ const Sources: FC<Props> = ({ repository, branches, selectedBranch, baseUrl }) =
   // redirect to default branch if no branch selected
   useEffect(() => {
     if (branches && branches.length > 0 && !selectedBranch) {
-      const defaultBranch = branches?.filter(b => b.defaultBranch === true)[0];
-      history.replace(`${baseUrl}/sources/${encodeURIComponent(defaultBranch.name)}/`);
+      const defaultBranch = branches?.filter((b) => b.defaultBranch === true)[0];
+      history.replace(
+        `${baseUrl}/sources/${defaultBranch ? encodeURIComponent(defaultBranch.name) : encodeURIComponent(branches[0].name)}/`
+      );
     }
   }, [branches, selectedBranch, history, baseUrl]);
   const { isLoading, error, data: file, isFetchingNextPage, fetchNextPage } = useSources(repository, {