diff --git a/ChangeLog b/ChangeLog
index cedafeeffb..e9774f174c 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,10 @@
+Mon Aug 27 22:39:08 2007  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* encoding.c (rb_enc_codelen): raises invalid sequence exception
+	  if ONIGENC_CODE_TO_MBCLEN() returns zero.  [ruby-dev:31661]
+
+	* encoding.c (rb_enc_mbclen): check invalid sequence.
+
 Mon Aug 27 20:27:59 2007  Masaki Suketa  <masaki.suketa@nifty.ne.jp>
 
 	* ext/win32ole/win32ole.c (ole_type_progid): fix the bug.
diff --git a/encoding.c b/encoding.c
index eed384fb0d..fc0aa3b945 100644
--- a/encoding.c
+++ b/encoding.c
@@ -216,6 +216,26 @@ rb_enc_strlen(const char *p, const char *e, rb_encoding *enc)
     return c;
 }
 
+int
+rb_enc_mbclen(const char *p, rb_encoding *enc)
+{
+    int n = ONIGENC_MBC_ENC_LEN(enc, (UChar*)p);
+    if (n == 0) {
+	rb_raise(rb_eArgError, "invalid mbstring sequence");
+    }
+    return n;
+}
+
+int
+rb_enc_codelen(int c, rb_encoding *enc)
+{
+    int n = ONIGENC_CODE_TO_MBCLEN(enc,c);
+    if (n == 0) {
+	rb_raise(rb_eArgError, "invalid mbstring sequence");
+    }
+    return n;
+}
+
 int
 rb_enc_toupper(int c, rb_encoding *enc)
 {
diff --git a/include/ruby/encoding.h b/include/ruby/encoding.h
index 0fd2e3ce52..805209d15a 100644
--- a/include/ruby/encoding.h
+++ b/include/ruby/encoding.h
@@ -50,8 +50,10 @@ rb_encoding * rb_enc_find(const char *name);
 #define rb_enc_mbmaxlen(enc) (enc)->max_enc_len
 
 /* ptr,encoding -> mbclen */
-#define rb_enc_mbclen(p,enc) ONIGENC_MBC_ENC_LEN(enc, (UChar*)p)
-#define rb_enc_codelen(c,enc) ONIGENC_CODE_TO_MBCLEN(enc,c)
+int rb_enc_mbclen(const char*, rb_encoding*);
+
+/* code,encoding -> codelen */
+int rb_enc_codelen(int, rb_encoding*);
 
 /* code,ptr,encoding -> write buf */
 #define rb_enc_mbcput(c,buf,enc) ONIGENC_CODE_TO_MBC(enc,c,(UChar*)buf)