diff --git a/CHANGELOG b/CHANGELOG
index d7f0b5ff..78e42f6d 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -19,6 +19,11 @@ HISTORY
 
   ++ New features:
 
+  2008-01-10 Frédéric Bernon
+  * tcpip.h, tcpip.c: add tcpip_callback_with_block function for the task #7490
+    "Add return value to sys_mbox_post". tcpip_callback is always defined as
+    "blocking" ("block" parameter = 1).
+
   2008-01-10 Frédéric Bernon
   * tcpip.h, tcpip.c, api.h, api_lib.c, api_msg.c, sockets.c: replace the field
     netconn::mbox (sys_mbox_t) per netconn::sem (sys_sem_t) for the task #7490
diff --git a/src/api/tcpip.c b/src/api/tcpip.c
index 4160a9b7..c7a3ca1f 100644
--- a/src/api/tcpip.c
+++ b/src/api/tcpip.c
@@ -349,10 +349,11 @@ tcpip_input(struct pbuf *p, struct netif *inp)
  *
  * @param f the function to call
  * @param ctx parameter passed to f
+ * @param block 1 to block until the request is posted, 0 to non-blocking mode
  * @return ERR_OK if the function was called, another err_t if not
  */
 err_t
-tcpip_callback(void (*f)(void *ctx), void *ctx)
+tcpip_callback_with_block(void (*f)(void *ctx), void *ctx, u8_t block)
 {
   struct tcpip_msg *msg;
 
@@ -365,7 +366,14 @@ tcpip_callback(void (*f)(void *ctx), void *ctx)
     msg->type = TCPIP_MSG_CALLBACK;
     msg->msg.cb.f = f;
     msg->msg.cb.ctx = ctx;
-    sys_mbox_post(mbox, msg);
+    if (block) {
+      sys_mbox_post(mbox, msg);
+    } else {
+      if (sys_mbox_trypost(mbox, msg) != ERR_OK) {
+        memp_free(MEMP_TCPIP_MSG_API, msg);
+        return ERR_MEM;
+      }
+    }
     return ERR_OK;
   }
   return ERR_VAL;
diff --git a/src/include/lwip/tcpip.h b/src/include/lwip/tcpip.h
index ee9ce3c4..fb2dbdeb 100644
--- a/src/include/lwip/tcpip.h
+++ b/src/include/lwip/tcpip.h
@@ -82,7 +82,9 @@ err_t tcpip_netifapi_lock(struct netifapi_msg *netifapimsg);
 #endif /* LWIP_TCPIP_CORE_LOCKING */
 #endif /* LWIP_NETIF_API */
 
-err_t tcpip_callback(void (*f)(void *ctx), void *ctx);
+err_t tcpip_callback_with_block(void (*f)(void *ctx), void *ctx, u8_t block);
+#define tcpip_callback(f,ctx) tcpip_callback_with_block(f,ctx,1)
+
 err_t tcpip_timeout(u32_t msecs, sys_timeout_handler h, void *arg);
 #define tcpip_untimeout(h, arg) tcpip_timeout(0xffffffff, h, arg)