diff --git a/diff-sha.sh b/diff-sha.sh
index 5e064a68ef1..9988824db89 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -208,13 +208,15 @@ else
     else
       echo "::debug::Fetching remote target branch..."
       # shellcheck disable=SC2086
-      git fetch $EXTRA_ARGS -u --progress --deepen="$INPUT_FETCH_DEPTH" origin "$TARGET_BRANCH" 1>/dev/null 2>&1
+      git fetch -u --progress $EXTRA_ARGS --depth="$INPUT_FETCH_DEPTH" origin +refs/heads/"$TARGET_BRANCH":refs/remotes/origin/"$TARGET_BRANCH" 1>/dev/null 2>&1
+
+      git branch --track "$TARGET_BRANCH" origin/"$TARGET_BRANCH" 1>/dev/null 2>&1 || true
 
       echo "::debug::Fetching remote current branch..."
       # shellcheck disable=SC2086
-      git fetch $EXTRA_ARGS -u --progress origin pull/"$GITHUB_EVENT_NUMBER"/head:"$CURRENT_BRANCH" 1>/dev/null 2>&1
+      git fetch $EXTRA_ARGS -u --progress --deepen="$INPUT_FETCH_DEPTH" origin "$CURRENT_BRANCH"
 
-      PREVIOUS_SHA=$(git merge-base origin/"$TARGET_BRANCH" "$CURRENT_SHA") && exit_status=$? || exit_status=$?
+      PREVIOUS_SHA=$(git merge-base "$TARGET_BRANCH" "$CURRENT_SHA") && exit_status=$? || exit_status=$?
     fi
 
     if [[ -z "$PREVIOUS_SHA" || "$PREVIOUS_SHA" == "$CURRENT_SHA" ]]; then
@@ -227,7 +229,7 @@ else
   fi
 
   if ! git diff --name-only --ignore-submodules=all "$PREVIOUS_SHA$DIFF$CURRENT_SHA" 1>/dev/null 2>&1; then
-    PREVIOUS_SHA=$(git rev-parse origin/"$TARGET_BRANCH") && exit_status=$? || exit_status=$?
+    PREVIOUS_SHA=$(git rev-parse "$TARGET_BRANCH") && exit_status=$? || exit_status=$?
     DIFF=".."
 
     if ! git diff --name-only --ignore-submodules=all "$PREVIOUS_SHA$DIFF$CURRENT_SHA" 1>/dev/null 2>&1; then