diff --git a/src/core/netif.c b/src/core/netif.c
index 4563082c..d971341c 100644
--- a/src/core/netif.c
+++ b/src/core/netif.c
@@ -500,6 +500,9 @@ void
 netif_set_ipaddr(struct netif *netif, const ip4_addr_t *ipaddr)
 {
   ip_addr_t old_addr;
+
+  LWIP_ERROR("netif_set_ipaddr: invalid netif", netif != NULL, return);
+
   /* Don't propagate NULL pointer (IPv4 ANY) to subsequent functions */
   if (ipaddr == NULL) {
     ipaddr = IP4_ADDR_ANY4;
@@ -564,6 +567,8 @@ netif_set_netmask(struct netif *netif, const ip4_addr_t *netmask)
 #endif
   LWIP_ASSERT_CORE_LOCKED();
 
+  LWIP_ERROR("netif_set_netmask: invalid netif", netif != NULL, return);
+
   /* Don't propagate NULL pointer (IPv4 ANY) to subsequent functions */
   if (netmask == NULL) {
     netmask = IP4_ADDR_ANY4;
@@ -623,6 +628,8 @@ netif_set_gw(struct netif *netif, const ip4_addr_t *gw)
 #endif
   LWIP_ASSERT_CORE_LOCKED();
 
+  LWIP_ERROR("netif_set_gw: invalid netif", netif != NULL, return);
+
   /* Don't propagate NULL pointer (IPv4 ANY) to subsequent functions */
   if (gw == NULL) {
     gw = IP4_ADDR_ANY4;
diff --git a/src/core/tcp_out.c b/src/core/tcp_out.c
index 91f56aad..fde928c2 100644
--- a/src/core/tcp_out.c
+++ b/src/core/tcp_out.c
@@ -1218,6 +1218,8 @@ tcp_build_sack_option(const struct tcp_pcb *pcb, u32_t *opts, u8_t num_sacks)
 static void
 tcp_build_wnd_scale_option(u32_t *opts)
 {
+  LWIP_ASSERT("tcp_build_wnd_scale_option: invalid opts", opts != NULL);
+
   /* Pad with one NOP option to make everything nicely aligned */
   opts[0] = PP_HTONL(0x01030300 | TCP_RCV_SCALE);
 }
@@ -1818,7 +1820,11 @@ tcp_output_alloc_header_common(u32_t ackno, u16_t optlen, u16_t datalen,
                         u16_t src_port, u16_t dst_port, u8_t flags, u16_t wnd)
 {
   struct tcp_hdr *tcphdr;
-  struct pbuf *p = pbuf_alloc(PBUF_IP, TCP_HLEN + optlen + datalen, PBUF_RAM);
+  struct pbuf *p;
+
+  LWIP_ASSERT("tcp_output_alloc_header: invalid pcb", pcb != NULL);
+
+  p = pbuf_alloc(PBUF_IP, TCP_HLEN + optlen + datalen, PBUF_RAM);
   if (p != NULL) {
     LWIP_ASSERT("check that first pbuf can hold struct tcp_hdr",
                 (p->len >= TCP_HLEN + optlen));