diff --git a/test/rubygems/test_gem_ext_cargo_builder_link_flag_converter.rb b/test/rubygems/test_gem_ext_cargo_builder_link_flag_converter.rb
index a3fef50d54..3693f63df6 100644
--- a/test/rubygems/test_gem_ext_cargo_builder_link_flag_converter.rb
+++ b/test/rubygems/test_gem_ext_cargo_builder_link_flag_converter.rb
@@ -25,7 +25,7 @@ class TestGemExtCargoBuilderLinkFlagConverter < Gem::TestCase
   }.freeze
 
   CASES.each do |test_name, (arg, expected)|
-    raise "duplicate test name" if instance_methods.include?(test_name)
+    raise "duplicate test name" if method_defined?(test_name)
 
     define_method(test_name) do
       assert_equal(expected, Gem::Ext::CargoBuilder::LinkFlagConverter.convert(arg))
diff --git a/test/rubygems/test_gem_package_tar_header_ractor.rb b/test/rubygems/test_gem_package_tar_header_ractor.rb
index 8f4cfb0072..5714064805 100644
--- a/test/rubygems/test_gem_package_tar_header_ractor.rb
+++ b/test/rubygems/test_gem_package_tar_header_ractor.rb
@@ -2,7 +2,7 @@
 
 require_relative "package/tar_test_case"
 
-unless Gem::Package::TarTestCase.instance_methods.include?(:assert_ractor)
+unless Gem::Package::TarTestCase.method_defined?(:assert_ractor)
   require "core_assertions"
   Gem::Package::TarTestCase.include Test::Unit::CoreAssertions
 end