diff --git a/.github/workflows/build-images.yml b/.github/workflows/build-images.yml
index 0d00ac0..ed9f2e4 100644
--- a/.github/workflows/build-images.yml
+++ b/.github/workflows/build-images.yml
@@ -19,6 +19,12 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v4
 
+      - name: Set lowercase owner name
+        run: |
+          # Use ZSH or Bash parameter expansion/tr to lowercase the string
+          OWNER_LC=$(echo "${{ github.repository_owner }}" | tr '[:upper:]' '[:lower:]')
+          echo "OWNER_LC=$OWNER_LC" >> $GITHUB_ENV
+
       - name: Log in to GHCR
         uses: docker/login-action@v3
         with:
@@ -31,11 +37,11 @@ jobs:
         with:
           context: ./docker/coturn
           push: true
-          tags: ghcr.io/${{ github.repository_owner,, }}/stoat-coturn:4.9.0-trixie
+          tags: ghcr.io/${{ env.OWNER_LC }}/stoat-coturn:4.9.0-trixie
 
       - name: Build and push Caddy WAF image
         uses: docker/build-push-action@v5
         with:
           context: ./docker/caddy
           push: true
-          tags: ghcr.io/${{ github.repository_owner,, }}/stoat-caddy-waf:latest
+          tags: ghcr.io/${{ env.OWNER_LC }}/stoat-caddy-waf:latest