diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 397e94489..e38699722 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -306,9 +306,17 @@ jobs:
         id: buildx
         uses: docker/setup-buildx-action@e468171a9de216ec08956ac3ada2f0791b6bd435 # v3.11.1
 
+      - name: Convert repository owner to lowercase
+        id: repoowner
+        run: echo "lowercase=$(echo ${{ github.repository_owner }} | tr '[:upper:]' '[:lower:]')" >> $GITHUB_OUTPUT
+
       - name: Generate test tag
         id: meta
-        run: echo "tags=ghcr.io/${{ github.repository_owner }}/stirling-pdf-test:${{ matrix.docker-rev }}-${{ github.sha }}" >> $GITHUB_OUTPUT
+        run: |
+          SAFE_NAME=$(echo "${{ matrix.docker-rev }}" | tr '[:upper:]' '[:lower:]' | sed 's/[^a-z0-9.-]/-/g')
+          TAG="ghcr.io/${{ steps.repoowner.outputs.lowercase }}/stirling-pdf-test:${SAFE_NAME}-${{ github.sha }}"
+          echo "tags=$TAG" >> $GITHUB_OUTPUT
+          echo "Using tag: $TAG"
 
       - name: Build and load multi-arch image
         uses: docker/build-push-action@263435318d21b8e681c14492fe198d362a7d2c83 # v6.18.0