diff --git a/ChangeLog b/ChangeLog
index 265cb4049b..1a0677c7e9 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Mon May 14 16:28:36 2012  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* parse.y (f_arglist): should reset lexical states after empty
+	  argument list with no parenthesis as well as parenthesized list,
+	  so that reserved name method definition work.  [ruby-dev:45626]
+	  [Bug #6403]
+
 Mon May 14 00:14:24 2012  CHIKANAGA Tomoyuki  <nagachika@ruby-lang.org>
 
 	* enumerator.c (lazy_take_func, lazy_take): multiple calls of
diff --git a/parse.y b/parse.y
index 098e946abd..9f9093b0bb 100644
--- a/parse.y
+++ b/parse.y
@@ -4451,6 +4451,8 @@ f_arglist	: '(' f_args rparen
 		| f_args term
 		    {
 			$$ = $1;
+			lex_state = EXPR_BEG;
+			command_start = TRUE;
 		    }
 		;
 
diff --git a/test/ruby/test_syntax.rb b/test/ruby/test_syntax.rb
index b792858090..7eef6d6066 100644
--- a/test/ruby/test_syntax.rb
+++ b/test/ruby/test_syntax.rb
@@ -176,6 +176,11 @@ class TestSyntax < Test::Unit::TestCase
     assert_valid_syntax("p begin 1.times do 1 end end", __FILE__, bug6419)
   end
 
+  def test_reserved_method_no_args
+    bug6403 = '[ruby-dev:45626]'
+    assert_valid_syntax("def self; :foo; end", __FILE__, bug6403)
+  end
+
   private
 
   def not_label(x) @result = x; @not_label ||= nil end