diff --git a/.gitignore b/.gitignore
index 340e704..b5aecf7 100644
--- a/.gitignore
+++ b/.gitignore
@@ -11,3 +11,5 @@
 
 # rspec failure tracking
 .rspec_status
+
+.ruby-version
diff --git a/.ruby-version b/.ruby-version
index 6a6a3d8..338a5b5 100644
--- a/.ruby-version
+++ b/.ruby-version
@@ -1 +1 @@
-2.6.1
+2.6.6
diff --git a/Gemfile.lock b/Gemfile.lock
index 0092aa8..e843cba 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    typerb (0.2.1)
+    typerb (0.3.0)
 
 GEM
   remote: https://rubygems.org/
diff --git a/lib/typerb.rb b/lib/typerb.rb
index 8db412c..da9b658 100644
--- a/lib/typerb.rb
+++ b/lib/typerb.rb
@@ -5,7 +5,7 @@
 require 'typerb/exceptional'
 
 module Typerb
-  refine Object do
+  refine BasicObject do
     def type!(*klasses)
       raise ArgumentError, 'provide at least one class' if klasses.empty?
       return self if klasses.any? { |kls| is_a?(kls) }
diff --git a/lib/typerb/version.rb b/lib/typerb/version.rb
index 1c57351..20c740b 100644
--- a/lib/typerb/version.rb
+++ b/lib/typerb/version.rb
@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 module Typerb
-  VERSION = '0.2.1'
+  VERSION = '0.3.0'
 end
diff --git a/spec/typerb_spec.rb b/spec/typerb_spec.rb
index 47460e9..c282bc2 100644
--- a/spec/typerb_spec.rb
+++ b/spec/typerb_spec.rb
@@ -152,6 +152,19 @@ def initialize(arg)
       end
       expect { kls.new('hello') }.to raise_error(ArgumentError, 'provide at least one class')
     end
+
+    it 'works with BasicObject' do
+      require 'tempfile'
+      kls = Class.new do
+        using Typerb
+
+        def initialize(arg)
+          arg.type!(Tempfile)
+          @arg = arg
+        end
+      end
+      expect { kls.new(Tempfile.new) }.not_to raise_error
+    end
   end
 
   context 'not_nil!' do