diff --git a/src/api/api_msg.c b/src/api/api_msg.c
index 96a4023c..fe97c012 100644
--- a/src/api/api_msg.c
+++ b/src/api/api_msg.c
@@ -512,8 +512,6 @@ accept_function(void *arg, struct tcp_pcb *newpcb, err_t err)
     sys_mbox_free(&newconn->recvmbox);
     sys_mbox_set_invalid(&newconn->recvmbox);
     netconn_free(newconn);
-    /* handle backlog counter */
-    tcp_backlog_accepted(newpcb);
     return ERR_MEM;
   } else {
     /* Register event with callback */
@@ -774,9 +772,6 @@ netconn_drain(struct netconn *conn)
       struct netconn *newconn = (struct netconn *)mem;
       /* Only tcp pcbs have an acceptmbox, so no need to check conn->type */
       /* pcb might be set to NULL already by err_tcp() */
-      if (newconn->pcb.tcp != NULL) {
-        tcp_backlog_accepted(newconn->pcb.tcp);
-      }
       /* drain recvmbox */
       netconn_drain(newconn);
       if (newconn->pcb.tcp != NULL) {
diff --git a/src/core/tcp.c b/src/core/tcp.c
index 145dbcd3..2285ecc6 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -194,9 +194,12 @@ void
 tcp_backlog_delayed(struct tcp_pcb* pcb)
 {
   LWIP_ASSERT("pcb != NULL", pcb != NULL);
-  if (pcb->listener != NULL) {
-    pcb->listener->accepts_pending++;
-    LWIP_ASSERT("accepts_pending != 0", pcb->listener->accepts_pending != 0);
+  if ((pcb->flags & TF_BACKLOGPEND) == 0) {
+    if (pcb->listener != NULL) {
+      pcb->listener->accepts_pending++;
+      LWIP_ASSERT("accepts_pending != 0", pcb->listener->accepts_pending != 0);
+      pcb->flags |= TF_BACKLOGPEND;
+    }
   }
 }
 
@@ -212,9 +215,12 @@ void
 tcp_backlog_accepted(struct tcp_pcb* pcb)
 {
   LWIP_ASSERT("pcb != NULL", pcb != NULL);
-  if (pcb->listener != NULL) {
-    LWIP_ASSERT("accepts_pending != 0", pcb->listener->accepts_pending != 0);
-    pcb->listener->accepts_pending--;
+  if ((pcb->flags & TF_BACKLOGPEND) != 0) {
+    if (pcb->listener != NULL) {
+      LWIP_ASSERT("accepts_pending != 0", pcb->listener->accepts_pending != 0);
+      pcb->listener->accepts_pending--;
+      pcb->flags &= ~TF_BACKLOGPEND;
+    }
   }
 }
 #endif /* TCP_LISTEN_BACKLOG */
@@ -470,6 +476,7 @@ tcp_abandon(struct tcp_pcb *pcb, int reset)
       tcp_segs_free(pcb->ooseq);
     }
 #endif /* TCP_QUEUE_OOSEQ */
+    tcp_backlog_accepted(pcb);
     if (send_rst) {
       LWIP_DEBUGF(TCP_RST_DEBUG, ("tcp_abandon: sending RST\n"));
       tcp_rst(seqno, ackno, &pcb->local_ip, &pcb->remote_ip, local_port, pcb->remote_port);
@@ -1599,7 +1606,9 @@ tcp_arg(struct tcp_pcb *pcb, void *arg)
 {
   /* This function is allowed to be called for both listen pcbs and
      connection pcbs. */
-  pcb->callback_arg = arg;
+  if (pcb != NULL) {
+    pcb->callback_arg = arg;
+  }
 }
 #if LWIP_CALLBACK_API
 
@@ -1613,8 +1622,10 @@ tcp_arg(struct tcp_pcb *pcb, void *arg)
 void
 tcp_recv(struct tcp_pcb *pcb, tcp_recv_fn recv)
 {
-  LWIP_ASSERT("invalid socket state for recv callback", pcb->state != LISTEN);
-  pcb->recv = recv;
+  if (pcb != NULL) {
+    LWIP_ASSERT("invalid socket state for recv callback", pcb->state != LISTEN);
+    pcb->recv = recv;
+  }
 }
 
 /**
@@ -1627,8 +1638,10 @@ tcp_recv(struct tcp_pcb *pcb, tcp_recv_fn recv)
 void
 tcp_sent(struct tcp_pcb *pcb, tcp_sent_fn sent)
 {
-  LWIP_ASSERT("invalid socket state for sent callback", pcb->state != LISTEN);
-  pcb->sent = sent;
+  if (pcb != NULL) {
+    LWIP_ASSERT("invalid socket state for sent callback", pcb->state != LISTEN);
+    pcb->sent = sent;
+  }
 }
 
 /**
@@ -1642,8 +1655,10 @@ tcp_sent(struct tcp_pcb *pcb, tcp_sent_fn sent)
 void
 tcp_err(struct tcp_pcb *pcb, tcp_err_fn err)
 {
-  LWIP_ASSERT("invalid socket state for err callback", pcb->state != LISTEN);
-  pcb->errf = err;
+  if (pcb != NULL) {
+    LWIP_ASSERT("invalid socket state for err callback", pcb->state != LISTEN);
+    pcb->errf = err;
+  }
 }
 
 /**
@@ -1657,7 +1672,7 @@ tcp_err(struct tcp_pcb *pcb, tcp_err_fn err)
 void
 tcp_accept(struct tcp_pcb *pcb, tcp_accept_fn accept)
 {
-  if (pcb->state == LISTEN) {
+  if ((pcb != NULL) && (pcb->state == LISTEN)) {
     struct tcp_pcb_listen *lpcb = (struct tcp_pcb_listen*)pcb;
     lpcb->accept = accept;
   }
@@ -1698,14 +1713,7 @@ tcp_pcb_purge(struct tcp_pcb *pcb)
 
     LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge\n"));
 
-#if TCP_LISTEN_BACKLOG
-    if (pcb->state == SYN_RCVD) {
-      tcp_backlog_accepted(pcb);
-      /* prevent executing this again: */
-      pcb->listener = NULL;
-    }
-#endif /* TCP_LISTEN_BACKLOG */
-
+    tcp_backlog_accepted(pcb);
 
     if (pcb->refused_data != NULL) {
       LWIP_DEBUGF(TCP_DEBUG, ("tcp_pcb_purge: data left on ->refused_data\n"));
diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index 7c7775d5..8f56b9f6 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -571,6 +571,7 @@ tcp_listen_input(struct tcp_pcb_listen *pcb)
     }
 #if TCP_LISTEN_BACKLOG
     pcb->accepts_pending++;
+    npcb->flags |= TF_BACKLOGPEND;
 #endif /* TCP_LISTEN_BACKLOG */
     /* Set up the new PCB. */
     ip_addr_copy(npcb->local_ip, *ip_current_dest_addr());
diff --git a/src/include/lwip/tcp.h b/src/include/lwip/tcp.h
index 9edcf169..7166485a 100644
--- a/src/include/lwip/tcp.h
+++ b/src/include/lwip/tcp.h
@@ -131,13 +131,17 @@ typedef err_t (*tcp_connected_fn)(void *arg, struct tcp_pcb *tpcb, err_t err);
 #define TCPWND16(x)             ((u16_t)LWIP_MIN((x), 0xFFFF))
 #define TCP_WND_MAX(pcb)        ((tcpwnd_size_t)(((pcb)->flags & TF_WND_SCALE) ? TCP_WND : TCPWND16(TCP_WND)))
 typedef u32_t tcpwnd_size_t;
-typedef u16_t tcpflags_t;
 #else
 #define RCV_WND_SCALE(pcb, wnd) (wnd)
 #define SND_WND_SCALE(pcb, wnd) (wnd)
 #define TCPWND16(x)             (x)
 #define TCP_WND_MAX(pcb)        TCP_WND
 typedef u16_t tcpwnd_size_t;
+#endif
+
+#if LWIP_WND_SCALE || TCP_LISTEN_BACKLOG
+typedef u16_t tcpflags_t;
+#else
 typedef u8_t tcpflags_t;
 #endif
 
@@ -207,6 +211,9 @@ struct tcp_pcb {
 #define TF_NAGLEMEMERR 0x80U   /* nagle enabled, memerr, try to output to prevent delayed ACK to happen */
 #if LWIP_WND_SCALE
 #define TF_WND_SCALE   0x0100U /* Window Scale option enabled */
+#endif
+#if TCP_LISTEN_BACKLOG
+#define TF_BACKLOGPEND 0x0200U /* If this is set, a connection pcb has increased the backlog on its listener */
 #endif
 
   /* the rest of the fields are in host byte order