diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5f705ae..96b9a67 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -10,6 +10,13 @@ on:
   workflow_call: {}
   workflow_dispatch: {}
 
+# Pushing three times to a branch used to queue three full matrices and run all of them. A newer
+# pull-request run supersedes the older one; a push to main is not cancelled, because main wants a
+# recorded result for every commit rather than only for the newest.
+concurrency:
+  group: ci-${{ github.event_name }}-${{ github.ref }}
+  cancel-in-progress: ${{ github.event_name == 'pull_request' }}
+
 jobs:
   ci:
     uses: Hawkynt/RepositoryTemplate/.github/workflows/dotnet-ci.yml@v1