diff --git a/.github/workflows/test-build.yml b/.github/workflows/test-build.yml
index 7fef7f50e..94b6c34c8 100644
--- a/.github/workflows/test-build.yml
+++ b/.github/workflows/test-build.yml
@@ -11,5 +11,7 @@ jobs:
     steps:
       - name: Checkout code
         uses: actions/checkout@master
+      - name: Set FARMOS_BRANCH environment variable
+        run: echo ::set-env name=FARMOS_BRANCH::${GITHUB_REF:11}
       - name: Build farmOS Docker image
-        run: docker build -t farmos-dev --build-arg FARMOS_REPO=https://github.com/${GITHUB_REPOSITORY} --build-arg FARMOS_BRANCH=${GITHUB_REF:11} docker/dev
+        run: docker build -t farmos-dev --build-arg FARMOS_REPO=https://github.com/${GITHUB_REPOSITORY} --build-arg FARMOS_BRANCH=${FARMOS_BRANCH} docker/dev