diff --git a/.builds/alpine.yml b/.builds/alpine.yml
index f8d75d8b1..0df721a06 100644
--- a/.builds/alpine.yml
+++ b/.builds/alpine.yml
@@ -58,3 +58,14 @@ tasks:
         -o public \
         "$include_dir/wlr/"
       zip -r ~/public.zip public/
+  - check-dco: |
+      set +x
+      cd wlroots
+      [ "${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-}" = "" ] && exit
+      git rev-list "$CI_MERGE_REQUEST_TARGET_BRANCH_NAME".. | while read -r rev; do
+        sob=$(git log -1 --pretty='%(trailers:key=Signed-off-by,separator= )')
+        if [ "$sob" = "" ]; then
+          echo "Commit $rev is missing a Signed-off-by trailer"
+          exit 1
+        fi
+      done
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 3b02ef16f..e5490fe34 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -1,4 +1,10 @@
 include: https://gitlab.freedesktop.org/emersion/dalligi/-/raw/master/templates/multi.yml
+workflow:
+  rules:
+    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
+    - if: $CI_COMMIT_BRANCH && $CI_OPEN_MERGE_REQUESTS
+      when: never
+    - if: $CI_COMMIT_BRANCH
 alpine:
   extends: .dalligi
   pages: true
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index d9c49f7c2..03b91fe47 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -101,6 +101,17 @@ message as well.
 
 See [How to Write a Git Commit Message] for more details.
 
+## Developer Certificate of Origin
+
+All commits must include a `Signed-off-by` trailer with your preferred name and
+email address which indicates that you agree to the [Developer Certificate of
+Origin]. If part of the patch has been authored by someone else, you should
+also gather `Signed-off-by` trailers from them in addition to your own trailer.
+These trailers certify that the commit can be submitted under the project's
+open-source license.
+
+The trailer can be added with `git commit -s`.
+
 ## Code Review
 
 When your changes are submitted for review, one or more core committers will
@@ -473,6 +484,7 @@ static void subsurface_handle_surface_destroy(struct wl_listener *listener,
 [freedesktop wiki]: https://gitlab.freedesktop.org/freedesktop/freedesktop/-/wikis/home
 [linear, "recipe" style]: https://www.bitsnbites.eu/git-history-work-log-vs-recipe/
 [git-rebase.io]: https://git-rebase.io/
+[Developer Certificate of Origin]: https://developercertificate.org/
 [reference issues]: https://docs.gitlab.com/ee/user/project/issues/managing_issues.html#closing-issues-automatically
 [Code of Conduct]: https://www.freedesktop.org/wiki/CodeOfConduct/
 [How to Write a Git Commit Message]: https://chris.beams.io/posts/git-commit/