diff --git a/ChangeLog b/ChangeLog
index 23df84c71f..6b749f1194 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Tue Dec 15 11:48:41 2009  NAKAMURA Usaku  <usa@ruby-lang.org>
+
+	* string.c (rb_str_inspect): wrong result of UTF-8 inspect because of
+	  the mistake of calculation.  reported by eban via IRC.
+
 Sun Dec 13 23:07:05 2009  NAKAMURA, Hiroshi  <nahi@ruby-lang.org>
 
 	* test/openssl/*: added some tests from jruby-openssl.
diff --git a/string.c b/string.c
index 924b5e3c92..f1db4eb00d 100644
--- a/string.c
+++ b/string.c
@@ -2719,7 +2719,7 @@ rb_str_inspect(str)
     while (p < pend) {
 	char c = *p++;
 	int len;
-	if (ismbchar(c) && p + (len = mbclen(c)) <= pend) {
+	if (ismbchar(c) && p - 1 + (len = mbclen(c)) <= pend) {
 	    rb_str_buf_cat(result, p - 1, len);
 	    p += len - 1;
 	}