diff --git a/ChangeLog b/ChangeLog
index a5a977c09c..00aad39c73 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+Thu Mar  6 00:34:00 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* sprintf.c (rb_str_format): size_t returned from strlen() can be
+	  unsigned.
+
 Thu Mar  6 00:31:39 2008  Nobuyoshi Nakada  <nobu@ruby-lang.org>
 
 	* struct.c (make_struct): preserve encoding of struct name.
diff --git a/sprintf.c b/sprintf.c
index a100946aa7..53d2d8bfc4 100644
--- a/sprintf.c
+++ b/sprintf.c
@@ -802,7 +802,7 @@ rb_str_format(int argc, const VALUE *argv, VALUE fmt)
 			    blen++;
 			    need--;
 			}
-			while (need-- - strlen(expr) > 0) {
+			while (need-- > strlen(expr)) {
 			    buf[blen++] = '0';
 			}
 			strncpy(&buf[blen], expr, strlen(expr));