diff --git a/lib/rails_admin/engine.rb b/lib/rails_admin/engine.rb
index 94dd90ff21..088b95bd73 100644
--- a/lib/rails_admin/engine.rb
+++ b/lib/rails_admin/engine.rb
@@ -29,9 +29,13 @@ class Engine < Rails::Engine
     end
 
     initializer 'RailsAdmin reload config in development' do
-      unless Rails.application.config.cache_classes
-        ActiveSupport::Reloader.before_class_unload do |cl|
-          RailsAdmin::Config.reset_all_models
+      if Rails.application.config.cache_classes
+        if defined?(ActiveSupport::Reloader)
+          ActiveSupport::Reloader.before_class_unload do
+            RailsAdmin::Config.reset_all_models
+          end
+          # else
+          # For Rails 4 not implemented
         end
       end
     end
diff --git a/spec/rails_admin/config_spec.rb b/spec/rails_admin/config_spec.rb
index 1928d1d603..97a98b86da 100644
--- a/spec/rails_admin/config_spec.rb
+++ b/spec/rails_admin/config_spec.rb
@@ -371,24 +371,30 @@ class Toggle < RailsAdmin::Config::Fields::Base
       expect(fields.map(&:name)).to match_array %i(id wins)
     end
 
-    it "updates model config when reloading code" do
-      Team.send(:rails_admin, &team_config)
-
-      # this simulates rails code reloading
-      Rails.application.config.cache_classes = false
-      RailsAdmin::Engine.initializers.select do |i|
-        i.name == "RailsAdmin reload config in development"
-      end.first.block.call
-      ActiveSupport::Reloader.new.tap do |instance|
-        instance.class_unload!
-      end
-      # /end
+    it "updates model config when reloading code for rails 5" do
+      if defined?(ActiveSupport::Reloader)
+        Team.send(:rails_admin, &team_config)
+
+        # this simulates rails code reloading
+        Rails.application.config.cache_classes = false
+        RailsAdmin::Engine.initializers.select do |i|
+          i.name == "RailsAdmin reload config in development"
+        end.first.block.call
+        if defined?(ActiveSupport::Reloader)
+          ActiveSupport::Reloader.new.tap(&:class_unload!)
+          # else
+          # for Rails 4 not imlemented
+        end
+        # /end
 
-      Team.send(:rails_admin, &team_config3)
-      expect(fields.map(&:name)).to match_array %i(wins)
+        Team.send(:rails_admin, &team_config3)
+        expect(fields.map(&:name)).to match_array %i(wins)
 
-      # restore setting to previous value
-      Rails.application.config.cache_classes = true
+        # restore setting to previous value
+        Rails.application.config.cache_classes = true
+        # else
+        # pending "for Rails 4 not implemented"
+      end
     end
   end
 end