diff --git a/ChangeLog b/ChangeLog
index 675f55409b..a31a883e15 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Fri Oct 30 18:54:04 2009  Yukihiro Matsumoto  <matz@ruby-lang.org>
+
+	* string.c (trnext): detect empty range and raise exception.
+	   [ruby-dev:39108]
+
 Fri Oct 30 17:01:46 2009  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* vm_eval.c (enum call_type): get rid of last comma.
diff --git a/string.c b/string.c
index 1dfab48cc1..e7f7e8673a 100644
--- a/string.c
+++ b/string.c
@@ -4642,7 +4642,17 @@ trnext(struct tr *t, rb_encoding *enc)
 		if (t->p < t->pend) {
 		    unsigned int c = rb_enc_codepoint_len(t->p, t->pend, &n, enc);
 		    t->p += n;
-		    if (t->now > c) continue;
+		    if (t->now > c) {
+			if (t->now < 0x80 && c < 0x80) {
+			    rb_raise(rb_eArgError,
+				     "invalid range \"%c-%c\" in string transliteration",
+				     t->now, c);
+			}
+			else {
+			    rb_raise(rb_eArgError, "invalid range in string transliteration");
+			}
+			continue; /* not reached */
+		    }
 		    t->gen = 1;
 		    t->max = c;
 		}