diff --git a/src/api/api_lib.c b/src/api/api_lib.c
index c61bf961..481b2e72 100644
--- a/src/api/api_lib.c
+++ b/src/api/api_lib.c
@@ -872,7 +872,7 @@ netconn_gethostbyname(const char *name, ip_addr_t *addr)
 void netconn_thread_init(void)
 {
   sys_sem_t *sem = LWIP_NETCONN_THREAD_SEM_GET();
-  if (!sys_sem_valid(sem)) {
+  if ((sem == NULL) || !sys_sem_valid(sem)) {
     /* call alloc only once */
     LWIP_NETCONN_THREAD_SEM_ALLOC();
     LWIP_ASSERT("LWIP_NETCONN_THREAD_SEM_ALLOC() failed", sys_sem_valid(LWIP_NETCONN_THREAD_SEM_GET()));
@@ -882,7 +882,7 @@ void netconn_thread_init(void)
 void netconn_thread_cleanup(void)
 {
   sys_sem_t *sem = LWIP_NETCONN_THREAD_SEM_GET();
-  if (sys_sem_valid(sem)) {
+  if ((sem != NULL) && sys_sem_valid(sem)) {
     /* call free only once */
     LWIP_NETCONN_THREAD_SEM_FREE();
   }