diff --git a/b2/subst.c b/b2/subst.c
index 8003ca3..5291c20 100644
--- a/b2/subst.c
+++ b/b2/subst.c
@@ -176,12 +176,8 @@ static const char *parse_var(struct chunk *c, const char *s)
 		c->type = ct_sub;
 		c->u.sub = *s-'0';
 	} else if (isalnum(*s)) {
-		char *tmp;
-
 		c->type = ct_var;
-		tmp = stralloc_n(s, t-s);
-		c->u.var = unique(tmp);
-		free(tmp);
+		c->u.var = unique_n(s, t-s);
 	} else {
 		c->type = ct_sub;
 		c->u.sub = 0;