diff --git a/.github/workflows/build-main.yaml b/.github/workflows/build-main.yaml
index 97f4b59ff..927794676 100644
--- a/.github/workflows/build-main.yaml
+++ b/.github/workflows/build-main.yaml
@@ -74,6 +74,13 @@ jobs:
         uses: docker/setup-buildx-action@v3
         with:
           driver: docker-container
+        env:
+          # buildx stores builder instances under $DOCKER_CONFIG/buildx/instances/.
+          # Create the builder in the SAME config the build step reads
+          # (runner.temp/.docker, seeded above and holding the OCIR auth); without
+          # this the builder lands in the default ~/.docker and the build step fails
+          # with `no builder "<name>" found`.
+          DOCKER_CONFIG: ${{ runner.temp }}/.docker
 
       - name: Build all images and write mode=max cache
         run: make build