diff --git a/diff-sha.sh b/diff-sha.sh
index cd139403..f7831edb 100644
--- a/diff-sha.sh
+++ b/diff-sha.sh
@@ -3,6 +3,7 @@
 set -eu
 
 INITIAL_COMMIT="false"
+GITHUB_OUTPUT=${GITHUB_OUTPUT:-""}
 
 echo "::group::changed-files-diff-sha"