diff --git a/Gemfile b/Gemfile
index e932169..ad76228 100644
--- a/Gemfile
+++ b/Gemfile
@@ -16,7 +16,7 @@ end
 
 group :development, :lint do
   gem 'overcommit', '>= 0.64'
-  gem 'rubocop', '~> 1.82.1'
+  gem 'rubocop', '~> 1.86.1'
   gem 'rubocop-minitest', '~> 0.39.1'
   gem 'rubocop-packaging', '~> 0.6.0'
   gem 'rubocop-performance', '~> 1.26.0'
diff --git a/lib/grift/mock_method.rb b/lib/grift/mock_method.rb
index ad5bd95..70f91ca 100644
--- a/lib/grift/mock_method.rb
+++ b/lib/grift/mock_method.rb
@@ -619,7 +619,7 @@ def class_instance
     #
     def method_defined?
       class_instance.method_defined?(@method_name, false) ||
-        class_instance.private_instance_methods(false).include?(@method_name)
+        class_instance.private_method_defined?(@method_name, false)
     end
 
     ##