diff --git a/.github/workflows/_prepare.yml b/.github/workflows/_prepare.yml
index 0a397c1..70d7e6b 100644
--- a/.github/workflows/_prepare.yml
+++ b/.github/workflows/_prepare.yml
@@ -28,7 +28,7 @@ jobs:
         run: |
           DEFAULT_BUILDER_REF="v0.6.54"
           BUILDER_REF="${{ inputs.builder_ref }}"
-          echo "ref=${BUILDER_REF:-$DEFAULT_BUILDER_REF=}" >> "$GITHUB_OUTPUT"
+          echo "ref=${BUILDER_REF:-$DEFAULT_BUILDER_REF}" >> "$GITHUB_OUTPUT"
       - name: Checkout build-emacs-for-macos repo
         uses: actions/checkout@v4
         with: