diff --git a/udp.c b/udp.c
index 0c01067..4be165f 100644
--- a/udp.c
+++ b/udp.c
@@ -644,12 +644,13 @@ void udp_reply_sock_handler(const struct ctx *c, union epoll_ref ref,
 	flow_sidx_t tosidx = flow_sidx_opposite(ref.flowside);
 	const struct flowside *toside = flowside_at_sidx(tosidx);
 	struct udp_flow *uflow = udp_at_sidx(ref.flowside);
-	int from_s = uflow->s[ref.flowside.sidei];
 	uint8_t topif = pif_at_sidx(tosidx);
-	int n, i;
+	int n, i, from_s;
 
 	ASSERT(!c->no_udp && uflow);
 
+	from_s = uflow->s[ref.flowside.sidei];
+
 	if (udp_sock_errs(c, from_s, events) < 0) {
 		flow_err(uflow, "Unrecoverable error on reply socket");
 		flow_err_details(uflow);