diff --git a/CHANGELOG b/CHANGELOG
index 3273d99d..f0d35c52 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -23,6 +23,10 @@ HISTORY
 
   ++ New features:
 
+  2007-04-11 Jonathan Larmour
+  * sys.h, api_lib.c: Provide new sys_mbox_tryfetch function. Require ports to provide new
+    sys_arch_mbox_tryfetch function to get a message if one is there.
+
   2007-04-06 Frédéric Bernon, Simon Goldschmidt
   * opt.h, tcpip.h, tcpip.c, netifapi.h, netifapi.c: New configuration option LWIP_NETIF_API
     allow to use thread-safe functions to add/remove netif in list, and to start/stop dhcp
diff --git a/src/api/api_lib.c b/src/api/api_lib.c
index dc4c2207..de47f92f 100644
--- a/src/api/api_lib.c
+++ b/src/api/api_lib.c
@@ -284,7 +284,7 @@ netconn_delete(struct netconn *conn)
 
   /* Drain the recvmbox. */
   if (conn->recvmbox != SYS_MBOX_NULL) {
-    while (sys_arch_mbox_fetch(conn->recvmbox, &mem, 1) != SYS_ARCH_TIMEOUT) {
+    while (sys_mbox_tryfetch(conn->recvmbox, &mem) != SYS_MBOX_EMPTY) {
       if (conn->type == NETCONN_TCP) {
         if(mem != NULL)
           pbuf_free((struct pbuf *)mem);
@@ -299,7 +299,7 @@ netconn_delete(struct netconn *conn)
 
   /* Drain the acceptmbox. */
   if (conn->acceptmbox != SYS_MBOX_NULL) {
-    while (sys_arch_mbox_fetch(conn->acceptmbox, &mem, 1) != SYS_ARCH_TIMEOUT) {
+    while (sys_mbox_tryfetch(conn->acceptmbox, &mem) != SYS_MBOX_EMPTY) {
       netconn_delete((struct netconn *)mem);
     }
     sys_mbox_free(conn->acceptmbox);
diff --git a/src/include/lwip/sys.h b/src/include/lwip/sys.h
index d631ad1b..50613c62 100644
--- a/src/include/lwip/sys.h
+++ b/src/include/lwip/sys.h
@@ -67,6 +67,11 @@ struct sys_timeo {u8_t dummy;};
 /** Return code for timeouts from sys_arch_mbox_fetch and sys_arch_sem_wait */
 #define SYS_ARCH_TIMEOUT 0xffffffffUL
 
+/* sys_mbox_tryfetch returns SYS_MBOX_EMPTY if appropriate.
+ * For now we use the same magic value, but we allow this to change in future.
+ */
+#define SYS_MBOX_EMPTY SYS_ARCH_TIMEOUT 
+
 typedef void (* sys_timeout_handler)(void *arg);
 
 struct sys_timeo {
@@ -116,6 +121,11 @@ u32_t sys_jiffies(void); /* since power up. */
 sys_mbox_t sys_mbox_new(void);
 void sys_mbox_post(sys_mbox_t mbox, void *msg);
 u32_t sys_arch_mbox_fetch(sys_mbox_t mbox, void **msg, u32_t timeout);
+#ifndef sys_arch_mbox_tryfetch /* Allow port to override with a macro */
+u32_t sys_arch_mbox_tryfetch(sys_mbox_t mbox, void **msg);
+#endif
+/* For now, we map straight to sys_arch implementation. */
+#define sys_mbox_tryfetch(mbox, msg) sys_arch_mbox_tryfetch(mbox, msg)
 void sys_mbox_free(sys_mbox_t mbox);
 #if LWIP_SO_RCVTIMEO
 void sys_mbox_fetch_timeout(sys_mbox_t mbox, void **msg, u32_t timeout);