diff --git a/ChangeLog b/ChangeLog
index 06894dd4feba26..e9d7f705d213f7 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Jan 14 18:24:13 2012  CHIKANAGA Tomoyuki  <nagachika00@gmail.com>
+
+	* error.c (exc_equal): clear rb_thread_t::errinfo when ignore
+	  an exception under rb_protect(). [ruby-core:41979] [Bug #5865]
+
 Sat Jan 14 12:02:55 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* sprintf.c (rb_enc_vsprintf): relaxed the restriction.  since the
diff --git a/error.c b/error.c
index 3b80a24bdd981c..03e22bfa3a7371 100644
--- a/error.c
+++ b/error.c
@@ -746,7 +746,10 @@ exc_equal(VALUE exc, VALUE obj)
 	CONST_ID(id_backtrace, "backtrace");
 
 	obj = rb_protect(try_convert_to_exception, obj, &status);
-	if (status || obj == Qundef) return Qfalse;
+	if (status || obj == Qundef) {
+	    rb_set_errinfo(Qnil);
+	    return Qfalse;
+	}
 	if (rb_obj_class(exc) != rb_obj_class(obj)) return Qfalse;
 	mesg = rb_check_funcall(obj, id_message, 0, 0);
 	if (mesg == Qundef) return Qfalse;
diff --git a/test/ruby/test_exception.rb b/test/ruby/test_exception.rb
index 22ac2aca1f617f..a44aef892b2420 100644
--- a/test/ruby/test_exception.rb
+++ b/test/ruby/test_exception.rb
@@ -379,6 +379,8 @@ def test_exception_in_name_error_to_str
     assert_nothing_raised(NameError, bug5575) do
       load(t.path)
     end
+  ensure
+    t.close(true) if t
   end
 
   def test_equal
@@ -386,4 +388,21 @@ def test_equal
     assert_equal(RuntimeError.new("a"), RuntimeError.new("a"), bug5865)
     assert_not_equal(RuntimeError.new("a"), StandardError.new("a"), bug5865)
   end
+
+  def test_exception_in_exception_equal
+    bug5865 = '[ruby-core:41979]'
+    t = Tempfile.new(["test_exception_in_exception_equal", ".rb"])
+    t.puts <<-EOC
+      o = Object.new
+      def o.exception(arg)
+      end
+      RuntimeError.new("a") == o
+    EOC
+    t.close
+    assert_nothing_raised(ArgumentError, bug5865) do
+      load(t.path)
+    end
+  ensure
+    t.close(true) if t
+  end
 end