diff --git a/.github/workflows/release-please-reusable.yml b/.github/workflows/release-please-reusable.yml
index a3da862..43d041d 100644
--- a/.github/workflows/release-please-reusable.yml
+++ b/.github/workflows/release-please-reusable.yml
@@ -116,6 +116,22 @@ jobs:
     permissions:
       contents: write
       pull-requests: write
+    # Serialize runs within the caller's repo. Unserialized, overlapping runs
+    # (a burst of merges, or one push GitHub delivers twice) each build a
+    # release commit, and the slower one fails updating the release branch
+    # ref. The group is repo-wide, not per-ref, because release-please always
+    # targets the default branch. `queue: max` keeps every run waiting its
+    # turn; without it GitHub keeps one pending run and cancels it when a
+    # newer one queues, which shows as a failed check on that commit. A
+    # caller that declares a group of this name deadlocks with this job.
+    concurrency:
+      group: release-please-reusable
+      queue: max
+      cancel-in-progress: false
+    # Bound a hung run: it holds the concurrency group, so no later run in
+    # the repo can start until it ends. The slowest caller's job takes just
+    # under five minutes.
+    timeout-minutes: 30
     # Hoist credentials to job env so step-level `if:` can read them — GitHub
     # allows the `env` context in step `if:` only when env is defined at the
     # workflow or job level, and the `secrets` context isn't allowed in `if:`
diff --git a/README.md b/README.md
index 432770d..67c9220 100644
--- a/README.md
+++ b/README.md
@@ -81,6 +81,8 @@ jobs:
 
 Treat `body`, `pr`, `prs` and `name` as untrusted text: they come from commit messages and PR titles. Pass them to a script through `env:` — never interpolate them directly into a `run:` block.
 
+The job runs in a repo-wide `release-please-reusable` concurrency group with `queue: max` and without `cancel-in-progress`, so overlapping pushes (a burst of merges, or a single push GitHub delivers twice) wait their turn instead of racing to update the release PR branch. Each queued run reads the branch's current HEAD, so a run that starts after its commit has been overtaken finds nothing left to do. The job times out after 30 minutes so a hung run cannot hold the group indefinitely. Don't declare a concurrency group of the same name in the caller; caller and callee would deadlock on it.
+
 Inputs:
 
 | Name                   | Type   | Default                          | Description                              |