diff --git a/releasenotes/notes/detect-gitlab-merge-error-69816ea60127b363.yaml b/releasenotes/notes/detect-gitlab-merge-error-69816ea60127b363.yaml
new file mode 100644
index 0000000000..a61b4129a4
--- /dev/null
+++ b/releasenotes/notes/detect-gitlab-merge-error-69816ea60127b363.yaml
@@ -0,0 +1,4 @@
+---
+fixes:
+  - |
+    Fix detection of the failed merge in gitlab driver.
diff --git a/tests/base.py b/tests/base.py
index a8ba5ea6b3..d0c5fb16ce 100644
--- a/tests/base.py
+++ b/tests/base.py
@@ -2156,7 +2156,7 @@ class FakeGitlabAPIClient(gitlabconnection.GitlabAPIClient):
             mr = self._get_mr(match)
             mr.mergeMergeRequest()
 
-        return {}, 200, "", "PUT"
+        return {'state': 'merged'}, 200, "", "PUT"
 
     def addProject(self, project):
         self.addProjectByName(project.name)
diff --git a/zuul/driver/gitlab/gitlabconnection.py b/zuul/driver/gitlab/gitlabconnection.py
index 2270278333..11edd1094c 100644
--- a/zuul/driver/gitlab/gitlabconnection.py
+++ b/zuul/driver/gitlab/gitlabconnection.py
@@ -404,6 +404,10 @@ class GitlabAPIClient():
         resp = self.put(self.baseurl + path, zuul_event_id=zuul_event_id)
         try:
             self._manage_error(*resp, zuul_event_id=zuul_event_id)
+            if resp[0]['state'] != 'merged':
+                raise MergeFailure(
+                    "Merge request merge failed: %s" % resp.get('merge_error')
+                )
         except GitlabAPIClientException as e:
             raise MergeFailure('Merge request merge failed: %s' % e)
         return resp[0]