diff --git a/gitlab/v4/objects.py b/gitlab/v4/objects.py
index 9e0256080..a7bad18bc 100644
--- a/gitlab/v4/objects.py
+++ b/gitlab/v4/objects.py
@@ -1213,6 +1213,12 @@ class ProjectMergeRequestManager(CRUDMixin, RESTManager):
                                'milestone_id'))
     _list_filters = ('iids', 'state', 'order_by', 'sort')
 
+    def _sanitize_data(self, data, action):
+        new_data = data.copy()
+        if 'labels' in data:
+            new_data['labels'] = ','.join(data['labels'])
+        return new_data
+
 
 class ProjectMilestone(SaveMixin, ObjectDeleteMixin, RESTObject):
     _short_print_attr = 'title'