diff --git a/ChangeLog b/ChangeLog
index d5a9230e91..59f28ca57c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Thu Mar 15 07:03:52 2012  Eric Hodel  <drbrain@segment7.net>
+
+	* vm_eval.c (check_funcall):  Raise ArgumentError if respond_to?
+	  requires more than three arguments. [Bug #6000]
+	* test/ruby/test_object.rb (class TestObject):  Test for respond_to?
+	  requiring more than three arguments.
+
 Thu Mar 15 06:08:06 2012  Marc-Andre Lafortune  <ruby-core@marc-andre.ca>
 
 	* include/ruby/intern.h: Add rb_check_arity, rb_error_arity [#6085]
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]'
 
diff --git a/vm_eval.c b/vm_eval.c
index 8bad08944d..398c344bc5 100644
--- a/vm_eval.c
+++ b/vm_eval.c
@@ -272,7 +272,10 @@ check_funcall(VALUE recv, ID mid, int argc, VALUE *argv)
 	VALUE args[2];
 	int arity = rb_method_entry_arity(me);
 
-	if (arity < 1 || arity > 3) arity = 2;
+	if (arity > 2)
+	    rb_raise(rb_eArgError, "respond_to? must accept 1 or 2 arguments (requires %d)", arity);
+
+	if (arity < 1) arity = 2;
 
 	args[0] = ID2SYM(mid);
 	args[1] = Qtrue;