diff --git a/b2/eval.c b/b2/eval.c
index 325940f..9cfa4c1 100644
--- a/b2/eval.c
+++ b/b2/eval.c
@@ -211,7 +211,7 @@ int eval_rel(const struct format *fmt, const char *s,
 	stop = strchr(s, 0);
 	if (!strip_unit(s, &stop, fmt->u.rel->u.abs, &mult))
 		return 0;
-	if (!relative(s, perc, &res->u.rel.plus, &res->u.rel.minus))
+	if (!relative(s, stop, &res->u.rel.plus, &res->u.rel.minus))
 		return 0;
 	res->u.rel.plus *= mult;
 	res->u.rel.minus *= mult;