diff --git a/diff-sha.sh b/diff-sha.sh
index ebde426c..f2ba2b87 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -111,7 +111,7 @@ if [[ -z $GITHUB_BASE_REF ]]; then
       fi
 
       if [[ -z "$PREVIOUS_SHA" || "$PREVIOUS_SHA" == "0000000000000000000000000000000000000000" ]]; then
-        PREVIOUS_SHA=$CURRENT_SHA
+        PREVIOUS_SHA=$(git rev-parse "$(git branch -r --sort=-committerdate | head -1 | xargs)")
       fi
 
       if [[ "$PREVIOUS_SHA" == "$CURRENT_SHA" ]]; then