1 files changed, 18 insertions, 0 deletions
diff --git a/test/ruby/test_object.rb b/test/ruby/test_object.rb
index f4a38e0ee3..271ab600a2 100644
--- a/test/ruby/test_object.rb
+++ b/test/ruby/test_object.rb
@@ -460,6 +460,24 @@ class TestObject < Test::Unit::TestCase
     assert_equal([[:respond_to?, :to_ary]], called, '[bug:6000]')
   end
 
+  def test_implicit_respond_to_arity_3
+    p = Object.new
+
+    called = []
+    p.singleton_class.class_eval do
+      define_method(:respond_to?) do |a, b, c|
+        called << [:respond_to?, a, b, c]
+        false
+      end
+    end
+
+    e = assert_raises(ArgumentError, '[bug:6000]') do
+      [[p]].flatten
+    end
+
+    assert_equal('respond_to? must accept 1 or 2 arguments (requires 3)',                        e.message)
+  end
+
   def test_method_missing_passed_block
     bug5731 = '[ruby-dev:44961]'