diff --git a/ChangeLog b/ChangeLog
index 6c27b43210..167350590c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Mon Jun  2 03:23:25 2008  NARUSE, Yui  <naruse@ruby-lang.org>
+
+	* enc/gb18030.c (gb18030_mbc_to_code): mask by 0x7FFFFFFF
+	  because OnigCodePoint will be used as 32bit signed int.
+	  Masking by 0x7FFFFFFF is ok on GB18030;
+	  Minumum 4bytes character is 0x81308130.
+
 Sun Jun  1 22:29:35 2008  NARUSE, Yui  <naruse@ruby-lang.org>
 
 	* rational.c (string_to_r_internal): use rb_isdigit.
diff --git a/enc/gb18030.c b/enc/gb18030.c
index 231b961188..f62a2394c9 100644
--- a/enc/gb18030.c
+++ b/enc/gb18030.c
@@ -166,7 +166,20 @@ gb18030_mbc_enc_len(const UChar* p, const UChar* e, OnigEncoding enc ARG_UNUSED)
 static OnigCodePoint
 gb18030_mbc_to_code(const UChar* p, const UChar* end, OnigEncoding enc)
 {
-  return onigenc_mbn_mbc_to_code(enc, p, end);
+  int c, i, len;
+  OnigCodePoint n;
+
+  len = enclen(enc, p, end);
+  n = (OnigCodePoint )(*p++);
+  if (len == 1) return n;
+
+  for (i = 1; i < len; i++) {
+    if (p >= end) break;
+    c = *p++;
+    n <<= 8;  n += c;
+  }
+  n &= 0x7FFFFFFF;
+  return n;
 }
 
 static int