diff --git a/.github/workflows/deploy.yml b/.github/workflows/deploy.yml
index 7c20beb6..6e2443dc 100644
--- a/.github/workflows/deploy.yml
+++ b/.github/workflows/deploy.yml
@@ -168,20 +168,13 @@ jobs:
         uses: docker/metadata-action@v5
         with:
           images: ghcr.io/${{ github.repository }}
-      - name: Short commit SHA
-        id: short
-        run: |
-          SHA="${{github.event.pull_request.head.sha}}${{ github.sha }}"
-          SHORT_SHA=${SHA:0:7}
-          echo "sha: $SHORT_SHA"
-          echo "sha=$SHORT_SHA" >> $GITHUB_OUTPUT
       - name: Build and publish Docker image
         uses: docker/build-push-action@v5
         with:
           context: .
           push: true
           build-args: |
-            WEBRCI_SHA=${{ steps.short.outputs.sha }}
+            WEBRCI_SHA=${{ github.sha }}
             MAKE_LIBS_TARGET=all
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
index 70006338..6a0efe49 100644
--- a/.github/workflows/test.yml
+++ b/.github/workflows/test.yml
@@ -47,19 +47,29 @@ jobs:
     steps:
       - name: Checkout repository
         uses: actions/checkout@v4
-      - name: Short commit SHA
-        id: short
+      - name: Obtain git ref for PR
+        if: ${{ github.event.pull_request.head.sha != '' }}
         run: |
-          SHA="${{github.event.pull_request.head.sha}}${{ github.sha }}"
-          SHORT_SHA=${SHA:0:7}
-          echo "sha: $SHORT_SHA"
-          echo "sha=$SHORT_SHA" >> $GITHUB_OUTPUT
+          REPO="https://github.com/${{github.event.pull_request.head.repo.full_name}}.git"
+          echo "repo: $REPO"
+          echo "repo=$REPO" >> $GITHUB_OUTPUT
+          SHA="${{ github.event.pull_request.head.sha }}"
+          echo "sha=$SHA" >> $GITHUB_OUTPUT
+      - name: Obtain git ref
+        if: ${{ github.event.pull_request.head.sha == '' }}
+        run: |
+          REPO="https://github.com/${{ github.repository }}.git"
+          echo "repo: $REPO"
+          echo "repo=$REPO" >> $GITHUB_OUTPUT
+          SHA="${{ github.sha }}"
+          echo "sha=$SHA" >> $GITHUB_OUTPUT
       - name: Build Docker image
         uses: docker/build-push-action@v5
         with:
           context: .
           push: false
           build-args: |
+            WEBRCI_REPO=${{ steps.short.outputs.repo }}
             WEBRCI_SHA=${{ steps.short.outputs.sha }}
             MAKE_LIBS_TARGET=default
   build-nix:
diff --git a/Dockerfile b/Dockerfile
index 120f158f..90b8932e 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -72,7 +72,8 @@ RUN rig add 4.4.0 --without-pak
 RUN /opt/R/current/bin/R -q -e 'install.packages("pak", lib = .Library)'
 
 # Download webR and configure for LLVM flang
-RUN git clone https://github.com/r-wasm/webr.git /opt/webr
+ARG WEBRCI_REPO="https://github.com/r-wasm/webr.git"
+RUN git clone ${WEBRCI_REPO} /opt/webr
 WORKDIR /opt/webr
 ARG WEBRCI_SHA=HEAD
 RUN git checkout ${WEBRCI_SHA}