diff --git a/get-modified-packages/action.yaml b/get-modified-packages/action.yaml
index 4831af82..72582460 100644
--- a/get-modified-packages/action.yaml
+++ b/get-modified-packages/action.yaml
@@ -17,6 +17,7 @@ runs:
     - name: Fetch the base branch with enough history for a common merge-base commit
       run: |
         git fetch origin ${{ github.event.pull_request.base.ref }}
+      shell: bash
 
     - name: Get modified packages
       id: get-modified-packages