diff --git a/src/api/api_lib.c b/src/api/api_lib.c
index 60678f88..ae1681e8 100644
--- a/src/api/api_lib.c
+++ b/src/api/api_lib.c
@@ -126,6 +126,9 @@ netconn_apimsg(tcpip_callback_fn fn, struct api_msg *apimsg)
 
 #if LWIP_NETCONN_SEM_PER_THREAD
   apimsg->op_completed_sem = LWIP_NETCONN_THREAD_SEM_GET();
+  if (!sys_sem_valid(apimsg->op_completed_sem)) {
+    return ERR_MEM;
+  }
 #endif /* LWIP_NETCONN_SEM_PER_THREAD */
 
   err = tcpip_send_msg_wait_sem(fn, apimsg, LWIP_API_MSG_SEM(apimsg));
@@ -1314,6 +1317,9 @@ netconn_gethostbyname(const char *name, ip_addr_t *addr)
 #endif /* LWIP_IPV4 && LWIP_IPV6 */
 #if LWIP_NETCONN_SEM_PER_THREAD
   API_VAR_REF(msg).sem = LWIP_NETCONN_THREAD_SEM_GET();
+  if (!sys_sem_valid(API_VAR_REF(msg).sem)) {
+    return ERR_MEM;
+  }
 #else /* LWIP_NETCONN_SEM_PER_THREAD*/
   err = sys_sem_new(API_EXPR_REF(API_VAR_REF(msg).sem), 0);
   if (err != ERR_OK) {
diff --git a/src/api/sockets.c b/src/api/sockets.c
index 341429de..145fdb0a 100644
--- a/src/api/sockets.c
+++ b/src/api/sockets.c
@@ -2068,6 +2068,10 @@ lwip_select(int maxfdp1, fd_set *readset, fd_set *writeset, fd_set *exceptset,
       API_SELECT_CB_VAR_REF(select_cb).exceptset = exceptset;
 #if LWIP_NETCONN_SEM_PER_THREAD
       API_SELECT_CB_VAR_REF(select_cb).sem = LWIP_NETCONN_THREAD_SEM_GET();
+      if (!sys_sem_valid(API_SELECT_CB_VAR_REF(select_cb).sem)) {
+        set_errno(ENOMEM);
+        return -1;
+      }
 #else /* LWIP_NETCONN_SEM_PER_THREAD */
       if (sys_sem_new(&API_SELECT_CB_VAR_REF(select_cb).sem, 0) != ERR_OK) {
         /* failed to create semaphore */
@@ -2413,6 +2417,11 @@ lwip_poll(struct pollfd *fds, nfds_t nfds, int timeout)
     API_SELECT_CB_VAR_REF(select_cb).poll_nfds = nfds;
 #if LWIP_NETCONN_SEM_PER_THREAD
     API_SELECT_CB_VAR_REF(select_cb).sem = LWIP_NETCONN_THREAD_SEM_GET();
+    if (!sys_sem_valid(API_SELECT_CB_VAR_REF(select_cb).sem)) {
+      set_errno(ENOMEM);
+      return -1;
+    }
+
 #else /* LWIP_NETCONN_SEM_PER_THREAD */
     if (sys_sem_new(&API_SELECT_CB_VAR_REF(select_cb).sem, 0) != ERR_OK) {
       /* failed to create semaphore */