lib/guard/plugin_util.rb

@@ -55,7 +55,7 @@ module Guard
     def initialize_plugin(options)
       klass = plugin_class
       fail "Could not load class: #{_constant_name.inspect}" unless klass
-      if klass.superclass.to_s == "Guard::Guard"
+      if klass.ancestors.include?(Guard)
         klass.new(options.delete(:watchers), options)
       else
         begin

spec/lib/guard/plugin_util_spec.rb

@@ -71,7 +71,7 @@ RSpec.describe Guard::PluginUtil do
     context "with a plugin inheriting from Guard::Plugin" do
       before do
-        expect(guard_rspec_class).to receive(:superclass) { ::Guard::Plugin }
+        expect(guard_rspec_class).to receive(:ancestors) { [::Guard::Plugin] }
       end
       it "instantiate the plugin using the new API" do