diff --git a/test/ulid/rails_test.rb b/test/ulid/rails_test.rb
index d12b9bc..a508713 100644
--- a/test/ulid/rails_test.rb
+++ b/test/ulid/rails_test.rb
@@ -91,7 +91,7 @@ def test_deserializes_the_value_back_to_an_ulid
   def test_auto_generate_primary_key
     user = User.create!
 
-    assert user.id.is_a? String
+    assert_kind_of String, user.id
     assert_equal 26, user.id.length
 
     id = user.id
diff --git a/ulid-rails.gemspec b/ulid-rails.gemspec
index 5dbd539..1590715 100644
--- a/ulid-rails.gemspec
+++ b/ulid-rails.gemspec
@@ -46,6 +46,6 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "pry-byebug"
   spec.add_development_dependency "rake"
   spec.add_development_dependency "minitest", "~> 5.0"
-  spec.add_development_dependency "rubocop-minitest"
-  spec.add_development_dependency "standard", "~> 1.32.0"
+  spec.add_development_dependency "rubocop-minitest", "0.34.5"
+  spec.add_development_dependency "standard", "~> 1.34.0"
 end