diff --git a/ChangeLog b/ChangeLog
index 7081133d80..3ef5b9d21f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sat Jan 14 12:00:20 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* error.c (exc_equal): ignore exceptions during implicit
+	  conversion.  [ruby-core:41979] [Bug #5865]
+
 Sat Jan 14 05:58:54 2012  Eric Hodel  <drbrain@segment7.net>
 
 	* io.c (rb_io_s_read):  Fix formatting of open_args comment.  Reported
@@ -18,6 +23,11 @@ Fri Jan 13 17:23:38 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* load.c (load_unlock): update loading table at once.
 
+Fri Jan 13 16:44:45 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* error.c (exc_equal): try implicit conversion for delegator.
+	  [ruby-core:41979] [Bug #5865]
+
 Fri Jan 13 03:46:53 2012  Akinori MUSHA  <knu@iDaemons.org>
 
 	* lib/shellwords.rb (Shellwords#shellescape): shellescape() now
diff --git a/error.c b/error.c
index 6844f992a6..3b80a24bdd 100644
--- a/error.c
+++ b/error.c
@@ -713,6 +713,14 @@ exc_set_backtrace(VALUE exc, VALUE bt)
     return rb_iv_set(exc, "bt", rb_check_backtrace(bt));
 }
 
+static VALUE
+try_convert_to_exception(VALUE obj)
+{
+    ID id_exception;
+    CONST_ID(id_exception, "exception");
+    return rb_check_funcall(obj, id_exception, 0, 0);
+}
+
 /*
  *  call-seq:
  *     exc == obj   -> true or false
@@ -732,10 +740,14 @@ exc_equal(VALUE exc, VALUE obj)
     CONST_ID(id_mesg, "mesg");
 
     if (rb_obj_class(exc) != rb_obj_class(obj)) {
+	int status = 0;
 	ID id_message, id_backtrace;
 	CONST_ID(id_message, "message");
 	CONST_ID(id_backtrace, "backtrace");
 
+	obj = rb_protect(try_convert_to_exception, obj, &status);
+	if (status || obj == Qundef) 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;
 	backtrace = rb_check_funcall(obj, id_backtrace, 0, 0);
diff --git a/test/ruby/test_exception.rb b/test/ruby/test_exception.rb
index 028391d1e6..22ac2aca1f 100644
--- a/test/ruby/test_exception.rb
+++ b/test/ruby/test_exception.rb
@@ -380,4 +380,10 @@ end.join
       load(t.path)
     end
   end
+
+  def test_equal
+    bug5865 = '[ruby-core:41979]'
+    assert_equal(RuntimeError.new("a"), RuntimeError.new("a"), bug5865)
+    assert_not_equal(RuntimeError.new("a"), StandardError.new("a"), bug5865)
+  end
 end