diff --git a/action.yml b/action.yml
index 6bea240..2b29ee9 100644
--- a/action.yml
+++ b/action.yml
@@ -116,6 +116,7 @@ runs:
 
     - name: Determine ref
       id: determine_ref
+      shell: bash
       run: |
         if [[ $GITHUB_REF == refs/heads/* ]]; then
           echo "REF_TYPE=branch" >> $GITHUB_ENV