diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ff9784f..098c4c4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -5,9 +5,10 @@ on:
       - master
   pull_request:
 
-# This allows a subsequently queued workflow run to interrupt previous runs
+# This allows a subsequently queued workflow run to interrupt previous runs, but
+# only in pull requests.
 concurrency:
-  group: '${{ github.workflow }} @ ${{ github.event.pull_request.head.label || github.head_ref || github.ref }}'
+  group: '${{ github.workflow }} @ ${{ github.head_ref || github.sha }}'
   cancel-in-progress: true
 
 jobs: