diff --git a/diff-sha.sh b/diff-sha.sh
index 2c583f28..ebfb22a2 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -158,6 +158,8 @@ else
     # shellcheck disable=SC2086
     git fetch -u --progress $EXTRA_ARGS --depth="$INPUT_FETCH_DEPTH" origin +refs/heads/"$TARGET_BRANCH":refs/remotes/origin/"$TARGET_BRANCH"
     git branch --track "$TARGET_BRANCH" origin/"$TARGET_BRANCH" 2>/dev/null || true
+  else
+    git fetch $EXTRA_ARGS -u --progress --depth="$INPUT_FETCH_DEPTH" origin +"$GITHUB_REF":refs/remotes/origin/"$CURRENT_BRANCH"
   fi
 
   echo "::debug::Getting HEAD SHA..."