diff --git a/diff-sha.sh b/diff-sha.sh
index 56a16e0d..443d3b59 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -212,9 +212,10 @@ else
       PREVIOUS_SHA=$(git rev-list -n 1 "$TARGET_BRANCH" 2>&1) && exit_status=$? || exit_status=$?
     fi
 
-    if [[ -z "$PREVIOUS_SHA" ]]; then
+    if [[ -z "$PREVIOUS_SHA" || "$PREVIOUS_SHA" == "$CURRENT_SHA" ]]; then
       PREVIOUS_SHA=$GITHUB_EVENT_PULL_REQUEST_BASE_SHA && exit_status=$? || exit_status=$?
     fi
+
     echo "::debug::Previous SHA: $PREVIOUS_SHA"
   else
     PREVIOUS_SHA=$INPUT_BASE_SHA && exit_status=$? || exit_status=$?