diff --git a/.github/workflows/ci.yaml b/.github/workflows/ci.yaml
index 2a7c0be..a7a8c4b 100644
--- a/.github/workflows/ci.yaml
+++ b/.github/workflows/ci.yaml
@@ -88,10 +88,17 @@ jobs:
             cache_scope: amber-helper-pr-${{ github.event.pull_request.number }}
             runner: ubuntu-24.04-arm
             arch: arm64
-    env:
-      IMAGE_REGISTRY: ghcr.io/${{ github.repository_owner }}
     steps:
       - uses: actions/checkout@v5
+      - name: Compute image registry (lowercase owner for GHCR)
+        id: registry
+        shell: bash
+        run: |
+          set -euo pipefail
+          owner_lc="$(printf '%s' '${{ github.repository_owner }}' | tr '[:upper:]' '[:lower:]')"
+          image_registry="ghcr.io/${owner_lc}"
+          echo "image_registry=${image_registry}" >> "$GITHUB_OUTPUT"
+          echo "IMAGE_REGISTRY=${image_registry}" >> "$GITHUB_ENV"
       - uses: docker/setup-buildx-action@v3
       - uses: docker/login-action@v3
         with:
@@ -107,7 +114,7 @@ jobs:
             BUILD_MODE=release
           platforms: linux/${{ matrix.arch }}
           push: true
-          tags: ${{ env.IMAGE_REGISTRY }}/${{ matrix.image }}:${{ github.sha }}-${{ matrix.arch }}
+          tags: ${{ steps.registry.outputs.image_registry }}/${{ matrix.image }}:${{ github.sha }}-${{ matrix.arch }}
           cache-from: |
             type=gha,scope=refs/heads/main-${{ matrix.image }}-${{ matrix.arch }}
             type=gha,scope=${{ matrix.cache_scope }}-${{ matrix.arch }}
@@ -121,9 +128,16 @@ jobs:
     permissions:
       contents: read
       packages: write
-    env:
-      IMAGE_REGISTRY: ghcr.io/${{ github.repository_owner }}
     steps:
+      - name: Compute image registry (lowercase owner for GHCR)
+        id: registry
+        shell: bash
+        run: |
+          set -euo pipefail
+          owner_lc="$(printf '%s' '${{ github.repository_owner }}' | tr '[:upper:]' '[:lower:]')"
+          image_registry="ghcr.io/${owner_lc}"
+          echo "image_registry=${image_registry}" >> "$GITHUB_OUTPUT"
+          echo "IMAGE_REGISTRY=${image_registry}" >> "$GITHUB_ENV"
       - uses: docker/setup-buildx-action@v3
       - uses: docker/login-action@v3
         with:
diff --git a/.github/workflows/publish.yaml b/.github/workflows/publish.yaml
index ef65a66..83ef984 100644
--- a/.github/workflows/publish.yaml
+++ b/.github/workflows/publish.yaml
@@ -48,10 +48,17 @@ jobs:
             file: docker/amber-compose-helper/Dockerfile
             runner: ubuntu-24.04-arm
             arch: arm64
-    env:
-      IMAGE_REGISTRY: ghcr.io/${{ github.repository_owner }}
     steps:
       - uses: actions/checkout@v5
+      - name: Compute image registry (lowercase owner for GHCR)
+        id: registry
+        shell: bash
+        run: |
+          set -euo pipefail
+          owner_lc="$(printf '%s' '${{ github.repository_owner }}' | tr '[:upper:]' '[:lower:]')"
+          image_registry="ghcr.io/${owner_lc}"
+          echo "image_registry=${image_registry}" >> "$GITHUB_OUTPUT"
+          echo "IMAGE_REGISTRY=${image_registry}" >> "$GITHUB_ENV"
       - uses: docker/setup-buildx-action@v3
       - uses: docker/login-action@v3
         with:
@@ -62,7 +69,7 @@ jobs:
         id: meta
         uses: docker/metadata-action@v5
         with:
-          images: ${{ env.IMAGE_REGISTRY }}/${{ matrix.image }}
+          images: ${{ steps.registry.outputs.image_registry }}/${{ matrix.image }}
           tags: |
             type=ref,event=branch
             type=ref,event=tag
@@ -92,9 +99,16 @@ jobs:
     permissions:
       contents: read
       packages: write
-    env:
-      IMAGE_REGISTRY: ghcr.io/${{ github.repository_owner }}
     steps:
+      - name: Compute image registry (lowercase owner for GHCR)
+        id: registry
+        shell: bash
+        run: |
+          set -euo pipefail
+          owner_lc="$(printf '%s' '${{ github.repository_owner }}' | tr '[:upper:]' '[:lower:]')"
+          image_registry="ghcr.io/${owner_lc}"
+          echo "image_registry=${image_registry}" >> "$GITHUB_OUTPUT"
+          echo "IMAGE_REGISTRY=${image_registry}" >> "$GITHUB_ENV"
       - uses: docker/setup-buildx-action@v3
       - uses: docker/login-action@v3
         with:
@@ -105,7 +119,7 @@ jobs:
         id: cli_meta
         uses: docker/metadata-action@v5
         with:
-          images: ${{ env.IMAGE_REGISTRY }}/amber-cli
+          images: ${{ steps.registry.outputs.image_registry }}/amber-cli
           tags: |
             type=ref,event=branch
             type=ref,event=tag
@@ -122,7 +136,7 @@ jobs:
         id: sidecar_meta
         uses: docker/metadata-action@v5
         with:
-          images: ${{ env.IMAGE_REGISTRY }}/amber-sidecar
+          images: ${{ steps.registry.outputs.image_registry }}/amber-sidecar
           tags: |
             type=ref,event=branch
             type=ref,event=tag
@@ -139,7 +153,7 @@ jobs:
         id: helper_meta
         uses: docker/metadata-action@v5
         with:
-          images: ${{ env.IMAGE_REGISTRY }}/amber-helper
+          images: ${{ steps.registry.outputs.image_registry }}/amber-helper
           tags: |
             type=ref,event=branch
             type=ref,event=tag