diff --git a/diff-sha.sh b/diff-sha.sh
index 8463c41a..896e0515 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -107,14 +107,14 @@ if [[ -z $GITHUB_EVENT_PULL_REQUEST_BASE_REF ]]; then
         if [[ "$GITHUB_EVENT_FORCED" == "false" || -z "$GITHUB_EVENT_FORCED" ]]; then
           PREVIOUS_SHA=$GITHUB_EVENT_BEFORE && exit_status=$? || exit_status=$?
         else
-          PREVIOUS_SHA=$(git rev-list -n 1 "HEAD~1") && exit_status=$? || exit_status=$?
+          PREVIOUS_SHA=$(git rev-list -n 1 "HEAD^") && exit_status=$? || exit_status=$?
         fi
       else
-        PREVIOUS_SHA=$(git rev-list -n 1 "HEAD~1") && exit_status=$? || exit_status=$?
+        PREVIOUS_SHA=$(git rev-list -n 1 "HEAD^") && exit_status=$? || exit_status=$?
       fi
 
       if [[ -z "$PREVIOUS_SHA" || "$PREVIOUS_SHA" == "0000000000000000000000000000000000000000" ]]; then
-        PREVIOUS_SHA=$(git rev-list -n 1 "HEAD~1") && exit_status=$? || exit_status=$?
+        PREVIOUS_SHA=$(git rev-list -n 1 "HEAD^") && exit_status=$? || exit_status=$?
       fi
 
       if [[ "$PREVIOUS_SHA" == "$CURRENT_SHA" ]]; then