diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 27036d0f..6dcb525a 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -6,12 +6,12 @@ on:
   pull_request:
     branches: [main, staging]
 
-# Queue new CI runs when a commit arrives on the same ref.
-# New runs queue instead of cancelling each other — prevents
-# the single self-hosted macOS arm64 runner from being monopolised.
+# Cancel in-progress CI runs when a new commit arrives on the same ref.
+# This prevents multiple stale runs from queuing behind each other and
+# monopolising the self-hosted macOS arm64 runner.
 concurrency:
   group: ci-${{ github.ref }}
-  cancel-in-progress: false
+  cancel-in-progress: true
 
 jobs:
   # Detect which paths changed so downstream jobs can skip when only