diff --git a/app/controllers/spree/admin/admin_controller_decorator.rb b/app/controllers/spree/admin/admin_controller_decorator.rb
index <HASH>..<HASH> 100644
--- a/app/controllers/spree/admin/admin_controller_decorator.rb
+++ b/app/controllers/spree/admin/admin_controller_decorator.rb
@@ -3,7 +3,11 @@ if defined?(Spree::Admin::BaseController)
   Spree::Admin::BaseController.class_eval do
     protected
       def model_class
-        "Spree::#{controller_name.classify}".constantize
+        const_name = "Spree::#{controller_name.classify}"
+        if Object.const_defined?(const_name)
+          return const_name.constantize
+        end
+        nil
       end
   end
 end
Only return a value from model_class method if constant is available

Fixes spree/spree#<I>