diff --git a/diff-sha.sh b/diff-sha.sh
index 5fa16a92..503343d6 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -165,7 +165,7 @@ else
     # shellcheck disable=SC2086
     git fetch $EXTRA_ARGS -u --progress --depth=$(( GITHUB_EVENT_PULL_REQUEST_COMMITS + 1 )) origin +"$GITHUB_REF":refs/remotes/origin/"$CURRENT_BRANCH" 1>/dev/null 2>&1
 
-    COMMON_ANCESTOR=$(git rev-list --first-parent --max-parents=0 --max-count=1 origin/"$CURRENT_BRANCH") && exit_status=$? || exit_status=$?
+    COMMON_ANCESTOR=$(git rev-list --ancestry-path "$CURRENT_BRANCH".."$TARGET_BRANCH") && exit_status=$? || exit_status=$?
 
     if [[ -z "$COMMON_ANCESTOR" ]]; then
       echo "::debug::Unable to locate a common ancestor for the current branch: $CURRENT_BRANCH"