diff --git a/src/core/altcp_tcp.c b/src/core/altcp_tcp.c
index 2d672cf9..67eccb86 100644
--- a/src/core/altcp_tcp.c
+++ b/src/core/altcp_tcp.c
@@ -53,6 +53,11 @@
 
 #include <string.h>
 
+#define ALTCP_TCP_ASSERT_CONN(conn, tpcb) do { \
+  LWIP_ASSERT("pcb mismatch", (conn)->state == tpcb); \
+  LWIP_ASSERT("conn->inner_conn == NULL", (conn)->inner_conn == NULL); } while(0)
+
+
 /* Variable prototype, the actual declaration is at the end of this file
    since it contains pointers to static functions declared here */
 extern const struct altcp_functions altcp_tcp_functions;
@@ -81,7 +86,7 @@ altcp_tcp_connected(void *arg, struct tcp_pcb *tpcb, err_t err)
 {
   struct altcp_pcb *conn = (struct altcp_pcb *)arg;
   if (conn) {
-    LWIP_ASSERT("pcb mismatch", conn->inner_conn == (struct altcp_pcb *)tpcb);
+    ALTCP_TCP_ASSERT_CONN(conn, tpcb);
     if (conn->connected) {
       return conn->connected(conn->arg, conn, err);
     }
@@ -94,7 +99,7 @@ altcp_tcp_recv(void *arg, struct tcp_pcb *tpcb, struct pbuf *p, err_t err)
 {
   struct altcp_pcb *conn = (struct altcp_pcb *)arg;
   if (conn) {
-    LWIP_ASSERT("pcb mismatch", conn->inner_conn == (struct altcp_pcb *)tpcb);
+    ALTCP_TCP_ASSERT_CONN(conn, tpcb);
     if (conn->recv) {
       return conn->recv(conn->arg, conn, p, err);
     }
@@ -111,7 +116,7 @@ altcp_tcp_sent(void *arg, struct tcp_pcb *tpcb, u16_t len)
 {
   struct altcp_pcb *conn = (struct altcp_pcb *)arg;
   if (conn) {
-    LWIP_ASSERT("pcb mismatch", conn->inner_conn == (struct altcp_pcb *)tpcb);
+    ALTCP_TCP_ASSERT_CONN(conn, tpcb);
     if (conn->sent) {
       return conn->sent(conn->arg, conn, len);
     }
@@ -124,7 +129,7 @@ altcp_tcp_poll(void *arg, struct tcp_pcb *tpcb)
 {
   struct altcp_pcb *conn = (struct altcp_pcb *)arg;
   if (conn) {
-    LWIP_ASSERT("pcb mismatch", conn->inner_conn == (struct altcp_pcb *)tpcb);
+    ALTCP_TCP_ASSERT_CONN(conn, tpcb);
     if (conn->poll) {
       return conn->poll(conn->arg, conn);
     }
@@ -159,7 +164,7 @@ static void
 altcp_tcp_setup(struct altcp_pcb *conn, struct tcp_pcb *tpcb)
 {
   altcp_tcp_setup_callbacks(conn, tpcb);
-  conn->inner_conn = (struct altcp_pcb *)tpcb;
+  conn->state = tpcb;
   conn->fns = &altcp_tcp_functions;
 }
 
@@ -187,7 +192,7 @@ static void
 altcp_tcp_set_poll(struct altcp_pcb *conn, u8_t interval)
 {
   if (conn != NULL) {
-    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->inner_conn;
+    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->state;
     tcp_poll(pcb, altcp_tcp_poll, interval);
   }
 }
@@ -196,7 +201,7 @@ static void
 altcp_tcp_recved(struct altcp_pcb *conn, u16_t len)
 {
   if (conn != NULL) {
-    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->inner_conn;
+    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->state;
     tcp_recved(pcb, len);
   }
 }
@@ -208,7 +213,7 @@ altcp_tcp_bind(struct altcp_pcb *conn, const ip_addr_t *ipaddr, u16_t port)
   if (conn == NULL) {
     return ERR_VAL;
   }
-  pcb = (struct tcp_pcb *)conn->inner_conn;
+  pcb = (struct tcp_pcb *)conn->state;
   return tcp_bind(pcb, ipaddr, port);
 }
 
@@ -220,7 +225,7 @@ altcp_tcp_connect(struct altcp_pcb *conn, const ip_addr_t *ipaddr, u16_t port, a
     return ERR_VAL;
   }
   conn->connected = connected;
-  pcb = (struct tcp_pcb *)conn->inner_conn;
+  pcb = (struct tcp_pcb *)conn->state;
   return tcp_connect(pcb, ipaddr, port, altcp_tcp_connected);
 }
 
@@ -232,10 +237,10 @@ altcp_tcp_listen(struct altcp_pcb *conn, u8_t backlog, err_t *err)
   if (conn == NULL) {
     return NULL;
   }
-  pcb = (struct tcp_pcb *)conn->inner_conn;
+  pcb = (struct tcp_pcb *)conn->state;
   lpcb = tcp_listen_with_backlog_and_err(pcb, backlog, err);
   if (lpcb != NULL) {
-    conn->inner_conn = (struct altcp_pcb *)lpcb;
+    conn->state = lpcb;
     tcp_accept(lpcb, altcp_tcp_accept);
     return conn;
   }
@@ -246,7 +251,7 @@ static void
 altcp_tcp_abort(struct altcp_pcb *conn)
 {
   if (conn != NULL) {
-    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->inner_conn;
+    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->state;
     tcp_abort(pcb);
   }
 }
@@ -258,7 +263,7 @@ altcp_tcp_close(struct altcp_pcb *conn)
   if (conn == NULL) {
     return ERR_VAL;
   }
-  pcb = (struct tcp_pcb *)conn->inner_conn;
+  pcb = (struct tcp_pcb *)conn->state;
   return tcp_close(pcb);
 }
 
@@ -269,7 +274,7 @@ altcp_tcp_shutdown(struct altcp_pcb *conn, int shut_rx, int shut_tx)
   if (conn == NULL) {
     return ERR_VAL;
   }
-  pcb = (struct tcp_pcb *)conn->inner_conn;
+  pcb = (struct tcp_pcb *)conn->state;
   return tcp_shutdown(pcb, shut_rx, shut_tx);
 }
 
@@ -280,7 +285,7 @@ altcp_tcp_write(struct altcp_pcb *conn, const void *dataptr, u16_t len, u8_t api
   if (conn == NULL) {
     return ERR_VAL;
   }
-  pcb = (struct tcp_pcb *)conn->inner_conn;
+  pcb = (struct tcp_pcb *)conn->state;
   return tcp_write(pcb, dataptr, len, apiflags);
 }
 
@@ -291,7 +296,7 @@ altcp_tcp_output(struct altcp_pcb *conn)
   if (conn == NULL) {
     return ERR_VAL;
   }
-  pcb = (struct tcp_pcb *)conn->inner_conn;
+  pcb = (struct tcp_pcb *)conn->state;
   return tcp_output(pcb);
 }
 
@@ -302,7 +307,7 @@ altcp_tcp_mss(struct altcp_pcb *conn)
   if (conn == NULL) {
     return 0;
   }
-  pcb = (struct tcp_pcb *)conn->inner_conn;
+  pcb = (struct tcp_pcb *)conn->state;
   return tcp_mss(pcb);
 }
 
@@ -313,7 +318,7 @@ altcp_tcp_sndbuf(struct altcp_pcb *conn)
   if (conn == NULL) {
     return 0;
   }
-  pcb = (struct tcp_pcb *)conn->inner_conn;
+  pcb = (struct tcp_pcb *)conn->state;
   return tcp_sndbuf(pcb);
 }
 
@@ -324,7 +329,7 @@ altcp_tcp_sndqueuelen(struct altcp_pcb *conn)
   if (conn == NULL) {
     return 0;
   }
-  pcb = (struct tcp_pcb *)conn->inner_conn;
+  pcb = (struct tcp_pcb *)conn->state;
   return tcp_sndqueuelen(pcb);
 }
 
@@ -332,7 +337,7 @@ static void
 altcp_tcp_setprio(struct altcp_pcb *conn, u8_t prio)
 {
   if (conn != NULL) {
-    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->inner_conn;
+    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->state;
     tcp_setprio(pcb, prio);
   }
 }
@@ -348,7 +353,7 @@ static err_t
 altcp_tcp_get_tcp_addrinfo(struct altcp_pcb *conn, int local, ip_addr_t *addr, u16_t *port)
 {
   if (conn) {
-    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->inner_conn;
+    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->state;
     return tcp_tcp_get_tcp_addrinfo(pcb, local, addr, port);
   }
   return ERR_VAL;
@@ -358,7 +363,7 @@ static ip_addr_t *
 altcp_tcp_get_ip(struct altcp_pcb *conn, int local)
 {
   if (conn) {
-    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->inner_conn;
+    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->state;
     if (pcb) {
       if (local) {
         return &pcb->local_ip;
@@ -375,7 +380,7 @@ static enum tcp_state
 altcp_tcp_dbg_get_tcp_state(struct altcp_pcb *conn)
 {
   if (conn) {
-    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->inner_conn;
+    struct tcp_pcb *pcb = (struct tcp_pcb *)conn->state;
     if (pcb) {
       return pcb->state;
     }