diff --git a/.github/workflows/publish-server-image.yml b/.github/workflows/publish-server-image.yml
index deb4b49..b9f70be 100644
--- a/.github/workflows/publish-server-image.yml
+++ b/.github/workflows/publish-server-image.yml
@@ -57,6 +57,9 @@ jobs:
       contents: read
     strategy:
       fail-fast: false
+      # One build at a time: parallel matrix jobs on the same self-hosted runner
+      # contend for a single buildkitd and lose the daemon mid-build.
+      max-parallel: 1
       matrix:
         include:
           - name: app