diff --git a/ChangeLog b/ChangeLog
index fae0911cc8..8affbb44bc 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,7 @@
+Mon Jan 28 15:33:23 2008  Tanaka Akira  <akr@fsij.org>
+
+	* enc/big5.c (big5_mbc_enc_len): validation implemented.
+
 Mon Jan 28 13:02:02 2008  Tanaka Akira  <akr@fsij.org>
 
 	* enc/euc_kr.c (euckr_mbc_enc_len): validation implemented.
diff --git a/enc/big5.c b/enc/big5.c
index 676e262252..442f9b5b63 100644
--- a/enc/big5.c
+++ b/enc/big5.c
@@ -48,10 +48,63 @@ static const int EncLen_BIG5[] = {
   2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 1
 };
 
+typedef enum { FAILURE = -2, ACCEPT = -1, S0 = 0, S1 } state_t;
+#define A ACCEPT
+#define F FAILURE
+static const signed char trans[][0x100] = {
+  { /* S0   0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f */
+    /* 0 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 1 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 2 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 3 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 4 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 5 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 6 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 7 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 8 */ F, F, F, F, F, F, F, F, F, F, F, F, F, F, F, F,
+    /* 9 */ F, F, F, F, F, F, F, F, F, F, F, F, F, F, F, F,
+    /* a */ F, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    /* b */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    /* c */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    /* d */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    /* e */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
+    /* f */ 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, F 
+  },
+  { /* S1   0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f */
+    /* 0 */ F, F, F, F, F, F, F, F, F, F, F, F, F, F, F, F,
+    /* 1 */ F, F, F, F, F, F, F, F, F, F, F, F, F, F, F, F,
+    /* 2 */ F, F, F, F, F, F, F, F, F, F, F, F, F, F, F, F,
+    /* 3 */ F, F, F, F, F, F, F, F, F, F, F, F, F, F, F, F,
+    /* 4 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 5 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 6 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* 7 */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, F,
+    /* 8 */ F, F, F, F, F, F, F, F, F, F, F, F, F, F, F, F,
+    /* 9 */ F, F, F, F, F, F, F, F, F, F, F, F, F, F, F, F,
+    /* a */ F, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* b */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* c */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* d */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* e */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, A,
+    /* f */ A, A, A, A, A, A, A, A, A, A, A, A, A, A, A, F 
+  }
+};
+#undef A
+#undef F
+
 static int
-big5_mbc_enc_len(const UChar* p, const UChar* end ARG_UNUSED, OnigEncoding enc ARG_UNUSED)
+big5_mbc_enc_len(const UChar* p, const UChar* e, OnigEncoding enc ARG_UNUSED)
 {
-  return EncLen_BIG5[*p];
+  int firstbyte = *p++;
+  state_t s = trans[0][firstbyte];
+#define RETURN(n) \
+    return s == ACCEPT ? ONIGENC_CONSTRUCT_MBCLEN_CHARFOUND(n) : \
+                         ONIGENC_CONSTRUCT_MBCLEN_INVALID()
+  if (s < 0) RETURN(1);
+  if (p == e) return ONIGENC_CONSTRUCT_MBCLEN_NEEDMORE(EncLen_BIG5[firstbyte]-1);
+  s = trans[s][*p++];
+  RETURN(2);
+#undef RETURN
 }
 
 static OnigCodePoint