diff --git a/ChangeLog b/ChangeLog
index 075814b5d4..6a9ab4f16b 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Mar 10 16:00:22 2011  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* parse.y (parser_encode_length): fix typo: the length of
+	  "-dos" and "-mac" is not 5 but 4.
+	  patched by James M. Lawrence [ruby-core:35476] fixes #4489
 Thu Mar 10 10:52:01 2011  NAKAMURA Usaku  <usa@ruby-lang.org>
 
 	* test/ruby/test_require.rb: setting too long string to ENV causes
diff --git a/parse.y b/parse.y
index 0e4a735dc6..b1408d8fd8 100644
--- a/parse.y
+++ b/parse.y
@@ -6230,7 +6230,7 @@ parser_encode_length(struct parser_params *parser, const char *name, long len)
 	if (rb_memcicmp(name + nlen + 1, "unix", 4) == 0)
 	    return nlen;
     }
-    if (len > 4 && name[nlen = len - 5] == '-') {
+    if (len > 4 && name[nlen = len - 4] == '-') {
 	if (rb_memcicmp(name + nlen + 1, "dos", 3) == 0)
 	    return nlen;
 	if (rb_memcicmp(name + nlen + 1, "mac", 3) == 0)