diff --git a/lib/gitlab/oauth/user.rb b/lib/gitlab/oauth/user.rb
index c5be884a89..9ad75e63a0 100644
--- a/lib/gitlab/oauth/user.rb
+++ b/lib/gitlab/oauth/user.rb
@@ -61,7 +61,9 @@ module Gitlab
         end
 
         def uid
-          auth.info.uid || auth.uid
+          uid = auth.info.uid || auth.uid
+          uid = uid.to_s unless uid.nil?
+          uid
         end
 
         def email