diff --git a/diff-sha.sh b/diff-sha.sh
index 5090dd2b..6573d955 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -227,7 +227,7 @@ else
       PREVIOUS_SHA=$GITHUB_EVENT_PULL_REQUEST_BASE_SHA
       
       if ! git diff --name-only --ignore-submodules=all "$PREVIOUS_SHA$DIFF$CURRENT_SHA" 1>/dev/null 2>&1; then
-        PREVIOUS_SHA=$(git merge-base "$PREVIOUS_SHA" "$CURRENT_SHA") && exit_status=$? || exit_status=$?
+        PREVIOUS_SHA=$(git merge-base "$TARGET_BRANCH" "$CURRENT_SHA") && exit_status=$? || exit_status=$?
       fi
     fi
 
@@ -249,7 +249,7 @@ else
         if git diff --name-only --ignore-submodules=all "$PREVIOUS_SHA$DIFF$CURRENT_SHA" 1>/dev/null 2>&1; then
           break
         else
-          NEW_PREVIOUS_SHA=$(git merge-base --fork-point "$PREVIOUS_SHA" "$CURRENT_SHA") && exit_status=$? || exit_status=$?
+          NEW_PREVIOUS_SHA=$(git merge-base --fork-point "$TARGET_BRANCH" "$CURRENT_SHA") && exit_status=$? || exit_status=$?
           
           if [[ -n "$NEW_PREVIOUS_SHA" ]]; then
             PREVIOUS_SHA=$NEW_PREVIOUS_SHA