diff --git a/CHANGELOG b/CHANGELOG
index c5b7a25f..c2621d72 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -19,6 +19,11 @@ HISTORY
 
   ++ New features:
 
+  2007-06-13 Frédéric Bernon, Simon Goldschmidt
+  * debug.h, api_msg.c: change LWIP_ERROR to use it to check errors like invalid
+    pointers or parameters, and let the possibility to redefined it in cc.h. Use
+    this macro to check "conn" parameter in api_msg.c functions.
+
   2007-06-11 Simon Goldschmidt
   * sockets.c, sockets.h: Added UDP lite support for sockets
 
diff --git a/src/api/api_lib.c b/src/api/api_lib.c
index b4244a43..3c967814 100644
--- a/src/api/api_lib.c
+++ b/src/api/api_lib.c
@@ -350,7 +350,7 @@ netconn_bind(struct netconn *conn, struct ip_addr *addr, u16_t port)
 {
   struct api_msg msg;
 
-  LWIP_ASSERT("netconn_bind: invalid conn", (conn != NULL));
+  LWIP_ERROR("netconn_bind: invalid conn", (conn == NULL), return ERR_ARG;);
 
   if (conn->type != NETCONN_TCP && conn->recvmbox == SYS_MBOX_NULL) {
     if ((conn->recvmbox = sys_mbox_new()) == SYS_MBOX_NULL) {
@@ -372,7 +372,7 @@ netconn_connect(struct netconn *conn, struct ip_addr *addr, u16_t port)
 {
   struct api_msg msg;
   
-  LWIP_ASSERT("netconn_connect: invalid conn", (conn != NULL));
+  LWIP_ERROR("netconn_connect: invalid conn", (conn == NULL), return ERR_ARG;);
 
   if (conn->recvmbox == SYS_MBOX_NULL) {
     if ((conn->recvmbox = sys_mbox_new()) == SYS_MBOX_NULL) {
@@ -394,7 +394,7 @@ netconn_disconnect(struct netconn *conn)
 {
   struct api_msg msg;
   
-  LWIP_ASSERT("netconn_disconnect: invalid conn", (conn != NULL));
+  LWIP_ERROR("netconn_disconnect: invalid conn", (conn == NULL), return ERR_ARG;);
 
   msg.function = do_disconnect;
   msg.msg.conn = conn;
@@ -408,7 +408,7 @@ netconn_listen(struct netconn *conn)
 {
   struct api_msg msg;
 
-  LWIP_ASSERT("netconn_listen: invalid conn", (conn != NULL));
+  LWIP_ERROR("netconn_listen: invalid conn", (conn == NULL), return ERR_ARG;);
 
   msg.function = do_listen;
   msg.msg.conn = conn;
@@ -421,8 +421,8 @@ netconn_accept(struct netconn *conn)
 {
   struct netconn *newconn;
 
-  LWIP_ASSERT("netconn_accept: invalid conn", (conn != NULL));
-  LWIP_ASSERT("netconn_accept: invalid acceptmbox", (conn->acceptmbox != SYS_MBOX_NULL));
+  LWIP_ERROR("netconn_accept: invalid conn",       (conn == NULL),                      return NULL;);
+  LWIP_ERROR("netconn_accept: invalid acceptmbox", (conn->acceptmbox == SYS_MBOX_NULL), return NULL;);
 
   #if LWIP_SO_RCVTIMEO
   if (sys_arch_mbox_fetch(conn->acceptmbox, (void *)&newconn, conn->recv_timeout)==SYS_ARCH_TIMEOUT) {
@@ -447,7 +447,7 @@ netconn_recv(struct netconn *conn)
   struct pbuf *p;
   u16_t len;
   
-  LWIP_ASSERT("netconn_recv: invalid conn", (conn != NULL));
+  LWIP_ERROR("netconn_recv: invalid conn",  (conn == NULL), return NULL;);
 
   if (conn->recvmbox == SYS_MBOX_NULL) {
     if ((conn->recvmbox = sys_mbox_new()) == SYS_MBOX_NULL) {
@@ -532,7 +532,7 @@ netconn_recv(struct netconn *conn)
     }
 #endif /* (LWIP_UDP || LWIP_RAW) */
   }
-    
+
   LWIP_DEBUGF(API_LIB_DEBUG, ("netconn_recv: received %p (err %d)\n", (void *)buf, conn->err));
 
   return buf;
@@ -553,7 +553,7 @@ netconn_send(struct netconn *conn, struct netbuf *buf)
 {
   struct api_msg msg;
 
-  LWIP_ASSERT("netconn_send: invalid conn", (conn != NULL));
+  LWIP_ERROR("netconn_send: invalid conn",  (conn == NULL), return ERR_ARG;);
 
   if (conn->err != ERR_OK) {
     return conn->err;
@@ -573,7 +573,7 @@ netconn_write(struct netconn *conn, const void *dataptr, u16_t size, u8_t copy)
   struct api_msg msg;
   u16_t len, sndbuf;
   
-  LWIP_ASSERT("netconn_write: invalid conn", (conn != NULL));
+  LWIP_ERROR("netconn_write: invalid conn",  (conn == NULL), return ERR_ARG;);
 
   if (conn->err != ERR_OK) {
     return conn->err;
@@ -603,7 +603,7 @@ netconn_write(struct netconn *conn, const void *dataptr, u16_t size, u8_t copy)
     } else {
       len = size;
     }
-    
+
     LWIP_DEBUGF(API_LIB_DEBUG, ("netconn_write: writing %d bytes (%d)\n", len, copy));
     msg.msg.msg.w.len = len;
     TCPIP_APIMSG(&msg);
@@ -619,7 +619,7 @@ netconn_write(struct netconn *conn, const void *dataptr, u16_t size, u8_t copy)
   }
  ret:
   conn->state = NETCONN_NONE;
-  
+
   return conn->err;
 }
 
@@ -628,7 +628,8 @@ netconn_close(struct netconn *conn)
 {
   struct api_msg msg;
 
-  LWIP_ASSERT("netconn_close: invalid conn", (conn != NULL));
+  LWIP_ERROR("netconn_close: invalid conn",  (conn == NULL), return ERR_ARG;);
+
 
   conn->state = NETCONN_CLOSE;
  again:
@@ -652,7 +653,7 @@ netconn_join_leave_group (struct netconn *conn,
 {
   struct api_msg msg;
 
-  LWIP_ASSERT("netconn_join_leave_group: invalid conn", (conn != NULL));
+  LWIP_ERROR("netconn_join_leave_group: invalid conn",  (conn == NULL), return ERR_ARG;);
 
   if (conn->err != ERR_OK) {
     return conn->err;
diff --git a/src/include/lwip/debug.h b/src/include/lwip/debug.h
index 1a0b0317..95e36bae 100644
--- a/src/include/lwip/debug.h
+++ b/src/include/lwip/debug.h
@@ -62,20 +62,23 @@
 #define LWIP_DBG_HALT    0x08U
 
 #ifndef LWIP_NOASSERT
-#  define LWIP_ASSERT(x,y) do { if(!(y)) LWIP_PLATFORM_ASSERT(x); } while(0)
-#else
-#  define LWIP_ASSERT(x,y) 
-#endif
+#define LWIP_ASSERT(x,y) do { if(!(y)) LWIP_PLATFORM_ASSERT(x); } while(0)
+#else  /* LWIP_NOASSERT */
+#define LWIP_ASSERT(x,y) 
+#endif /* LWIP_NOASSERT */
+
+/** print "m" message only if "e" is true, and execute "h" expression */
+#ifndef LWIP_ERROR
+#define LWIP_ERROR(m,e,h) do { if (e) { LWIP_PLATFORM_ASSERT(m); h;}} while(0)
+#endif /* LWIP_ERROR */
 
 #ifdef LWIP_DEBUG
 /** print debug message only if debug message type is enabled...
  *  AND is of correct type AND is at least LWIP_DBG_LEVEL
  */
-#  define LWIP_DEBUGF(debug,x) do { if (((debug) & LWIP_DBG_ON) && ((debug) & LWIP_DBG_TYPES_ON) && ((s16_t)((debug) & LWIP_DBG_MASK_LEVEL) >= LWIP_DBG_MIN_LEVEL)) { LWIP_PLATFORM_DIAG(x); if ((debug) & LWIP_DBG_HALT) while(1); } } while(0)
-#  define LWIP_ERROR(x)   do { LWIP_PLATFORM_DIAG(x); } while(0)  
-#else /* LWIP_DEBUG */
-#  define LWIP_DEBUGF(debug,x) 
-#  define LWIP_ERROR(x)  
+#define LWIP_DEBUGF(debug,x) do { if (((debug) & LWIP_DBG_ON) && ((debug) & LWIP_DBG_TYPES_ON) && ((s16_t)((debug) & LWIP_DBG_MASK_LEVEL) >= LWIP_DBG_MIN_LEVEL)) { LWIP_PLATFORM_DIAG(x); if ((debug) & LWIP_DBG_HALT) while(1); } } while(0)
+#else  /* LWIP_DEBUG */
+#define LWIP_DEBUGF(debug,x) 
 #endif /* LWIP_DEBUG */
 
 #endif /* __LWIP_DEBUG_H__ */