diff --git a/gems/gitlab-housekeeper/lib/gitlab/housekeeper/gitlab_client.rb b/gems/gitlab-housekeeper/lib/gitlab/housekeeper/gitlab_client.rb
index 91f1bcf8944950c9851c47e7e55f8220b006a948..f78320ea707f584127c5d0e28a42f5174f1a56e5 100644
--- a/gems/gitlab-housekeeper/lib/gitlab/housekeeper/gitlab_client.rb
+++ b/gems/gitlab-housekeeper/lib/gitlab/housekeeper/gitlab_client.rb
@@ -178,7 +178,7 @@ def update_existing_merge_request(
       end
 
       def usernames_to_ids(usernames)
-        usernames.map do |username|
+        Array(usernames).map do |username|
           data = request(:get, "/users", query: { username: username })
           data[0]['id']
         end