diff --git a/tcp.c b/tcp.c
index e606603..05a430b 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2326,7 +2326,9 @@ void tcp_listen_handler(struct ctx *c, union epoll_ref ref,
 	union flow *flow;
 	int s;
 
-	if (c->no_tcp || !(flow = flow_alloc()))
+	ASSERT(!c->no_tcp);
+
+	if (!(flow = flow_alloc()))
 		return;
 
 	s = accept4(ref.fd, &sa.sa, &sl, SOCK_NONBLOCK);
@@ -2379,8 +2381,7 @@ void tcp_timer_handler(struct ctx *c, union epoll_ref ref)
 	struct itimerspec check_armed = { { 0 }, { 0 } };
 	struct tcp_tap_conn *conn = CONN(ref.flow);
 
-	if (c->no_tcp)
-		return;
+	ASSERT(!c->no_tcp);
 
 	/* We don't reset timers on ~ACK_FROM_TAP_DUE, ~ACK_TO_TAP_DUE. If the
 	 * timer is currently armed, this event came from a previous setting,
@@ -2442,6 +2443,7 @@ void tcp_sock_handler(struct ctx *c, union epoll_ref ref, uint32_t events)
 {
 	struct tcp_tap_conn *conn = CONN(ref.flowside.flow);
 
+	ASSERT(!c->no_tcp);
 	ASSERT(conn->f.type == FLOW_TCP);
 	ASSERT(conn->f.pif[ref.flowside.side] != PIF_TAP);
 
@@ -2541,6 +2543,8 @@ int tcp_sock_init(const struct ctx *c, sa_family_t af, const void *addr,
 {
 	int r4 = FD_REF_MAX + 1, r6 = FD_REF_MAX + 1;
 
+	ASSERT(!c->no_tcp);
+
 	if (af == AF_UNSPEC && c->ifi4 && c->ifi6)
 		/* Attempt to get a dual stack socket */
 		if (tcp_sock_init_af(c, AF_UNSPEC, port, addr, ifname) >= 0)
@@ -2618,6 +2622,8 @@ static void tcp_ns_sock_init6(const struct ctx *c, in_port_t port)
  */
 void tcp_ns_sock_init(const struct ctx *c, in_port_t port)
 {
+	ASSERT(!c->no_tcp);
+
 	if (c->ifi4)
 		tcp_ns_sock_init4(c, port);
 	if (c->ifi6)
@@ -2706,6 +2712,8 @@ int tcp_init(struct ctx *c)
 	unsigned int b, optv = 0;
 	int s;
 
+	ASSERT(!c->no_tcp);
+
 	for (b = 0; b < TCP_HASH_TABLE_SIZE; b++)
 		tc_hash[b] = FLOW_SIDX_NONE;
 
diff --git a/udp.c b/udp.c
index 187483f..fbf3ce7 100644
--- a/udp.c
+++ b/udp.c
@@ -749,7 +749,9 @@ static int udp_sock_recv(const struct ctx *c, int s, uint32_t events,
 	 */
 	int n = (c->mode == MODE_PASTA ? 1 : UDP_MAX_FRAMES);
 
-	if (c->no_udp || !(events & EPOLLIN))
+	ASSERT(!c->no_udp);
+
+	if (!(events & EPOLLIN))
 		return 0;
 
 	n = recvmmsg(s, mmh, n, 0, NULL);
@@ -849,10 +851,11 @@ int udp_tap_handler(struct ctx *c, uint8_t pif,
 	in_port_t src, dst;
 	socklen_t sl;
 
-	(void)c;
 	(void)saddr;
 	(void)pif;
 
+	ASSERT(!c->no_udp);
+
 	uh = packet_get(p, idx, 0, sizeof(*uh), NULL);
 	if (!uh)
 		return 1;
@@ -1026,6 +1029,8 @@ int udp_sock_init(const struct ctx *c, int ns, sa_family_t af,
 				     .orig = true, .port = port };
 	int s, r4 = FD_REF_MAX + 1, r6 = FD_REF_MAX + 1;
 
+	ASSERT(!c->no_udp);
+
 	if (ns)
 		uref.pif = PIF_SPLICE;
 	else
@@ -1214,6 +1219,8 @@ void udp_timer(struct ctx *c, const struct timespec *now)
 	unsigned int i;
 	long *word, tmp;
 
+	ASSERT(!c->no_udp);
+
 	if (c->mode == MODE_PASTA) {
 		if (c->udp.fwd_out.f.mode == FWD_AUTO) {
 			fwd_scan_ports_udp(&c->udp.fwd_out.f, &c->udp.fwd_in.f,
@@ -1257,6 +1264,8 @@ v6:
  */
 int udp_init(struct ctx *c)
 {
+	ASSERT(!c->no_udp);
+
 	udp_iov_init(c);
 
 	udp_invert_portmap(&c->udp.fwd_in);