diff --git a/app/models/user.rb b/app/models/user.rb
index a17e4e9baa4..cd4792ea810 100644
--- a/app/models/user.rb
+++ b/app/models/user.rb
@@ -472,7 +472,7 @@ class User < ActiveRecord::Base
     # TODO it may be worth caching this in a distributed cache, should be benched
     if SiteSetting.external_system_avatars_enabled
       url = SiteSetting.external_system_avatars_url.dup
-      url.gsub! "{color}", letter_avatar_color(username)
+      url.gsub! "{color}", letter_avatar_color(username.downcase)
       url.gsub! "{username}", username
       url.gsub! "{first_letter}", username[0].downcase
       url