diff --git a/.github/workflows/deploy.yml b/.github/workflows/deploy.yml
index 1cf6952..eba58c0 100644
--- a/.github/workflows/deploy.yml
+++ b/.github/workflows/deploy.yml
@@ -7,6 +7,14 @@ on:
 permissions:
   contents: write
 
+# Use a single shared concurrency group so all runs that write to gh-pages are
+# serialised. A per-ref group still allows concurrent writes from different
+# triggers and causes rebase conflicts on the gh-pages branch.
+# cancel-in-progress: false ensures queued runs still execute.
+concurrency:
+  group: gh-pages
+  cancel-in-progress: false
+
 jobs:
   deploy:
     runs-on: ubuntu-latest
diff --git a/.github/workflows/preview.yml b/.github/workflows/preview.yml
index 9ceca9b..9e465c9 100644
--- a/.github/workflows/preview.yml
+++ b/.github/workflows/preview.yml
@@ -12,7 +12,15 @@ permissions:
   contents: write
   pull-requests: write
 
-concurrency: preview-${{ github.ref }}
+# Use a single shared concurrency group so all runs that write to gh-pages are
+# serialised. "preview-${{ github.ref }}" only serialises per PR, which still
+# allows concurrent writes from different PRs (or synchronize vs. closed events)
+# and causes "remote contains work not present locally" / rebase conflicts.
+# cancel-in-progress: false ensures queued runs still execute (important for
+# the "closed" event that removes a preview).
+concurrency:
+  group: gh-pages
+  cancel-in-progress: false
 
 jobs:
   deploy-preview: