diff --git a/vendor/plugins/authentication/app/models/user.rb b/vendor/plugins/authentication/app/models/user.rb
index fa3ff81a32..a50bb06714 100644
--- a/vendor/plugins/authentication/app/models/user.rb
+++ b/vendor/plugins/authentication/app/models/user.rb
@@ -59,7 +59,9 @@ def can_delete?(user_to_delete = self)
   end
 
   def add_role(role_to_add)
-    roles << Role[role_to_add]
+    unless self.has_role?(role = Role[role_to_add])
+      roles << role
+    end
   end
 
   def has_role?(role)