diff --git a/ChangeLog b/ChangeLog
index 97db6d8bce..0b7ba03833 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Sun Apr 27 23:13:20 2003  Nobuyoshi Nakada  <nobu.nokada@softhome.net>
+
+	* string.c (rb_str_to_i): disallow negative radix.
+	  [ruby-dev:20087]
+
 Sat Apr 26 23:34:42 2003  Yukihiro Matsumoto  <matz@ruby-lang.org>
 
 	* parse.y (open_args): warning message changed to "don't put space
diff --git a/string.c b/string.c
index 733a7dfc30..42177887a8 100644
--- a/string.c
+++ b/string.c
@@ -1836,6 +1836,9 @@ rb_str_to_i(argc, argv, str)
     if (argc == 0) base = 10;
     else base = NUM2INT(b);
 
+    if (base < 0) {
+	rb_raise(rb_eArgError, "illegal radix %d", base);
+    }
     return rb_str_to_inum(str, base, Qfalse);
 }