diff --git a/ChangeLog b/ChangeLog
index b8faf5513a..038922dffa 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Oct 10 03:41:31 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* sprintf.c (rb_str_format): check if codepoint for %c is valid.
+	  [ruby-dev:36691]
+
 Fri Oct 10 01:55:48 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* encoding.c (enc_names): minor improvement.
diff --git a/sprintf.c b/sprintf.c
index 0085cfc176..34152b1704 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -618,7 +618,7 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
 		    c = NUM2INT(val);
 		}
 		n = rb_enc_codelen(c, enc);
-		if (n == 0) {
+		if (n <= 0) {
 		    rb_raise(rb_eArgError, "invalid character");
 		}
 		if (!(flags & FWIDTH)) {