diff --git a/lib/sequel/plugins/devise.rb b/lib/sequel/plugins/devise.rb
index 1f1983d..7072d0d 100644
--- a/lib/sequel/plugins/devise.rb
+++ b/lib/sequel/plugins/devise.rb
@@ -48,7 +48,7 @@ def update_attribute(key, value)
         private
 
         def devise_safe_values
-          values.delete_if{|k, v| devise_safe_keys.include?(k) || k =~ /password/i }
+          values.dup.delete_if{|k, v| devise_safe_keys.include?(k) || k =~ /password/i }
         end
 
         def devise_safe_keys