diff --git a/CHANGELOG b/CHANGELOG
index bd310580..4f4cc643 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -166,6 +166,11 @@ HISTORY
 
   ++ Bug fixes:
 
+  2007-05-22 Frédéric Bernon
+  * api.h, api_lib.c, api_msg.h, api_msg.c: change the struct api_msg_msg to see
+    which parameters are used by which do_xxx function, and to avoid "misusing"
+    parameters (patch #5938).
+
   2007-05-22 Simon Goldschmidt
   * api_lib.c, api_msg.c, raw.c, api.h, api_msg.h, raw.h: Included patch #5938:
     changed raw_pcb.protocol from u16_t to u8_t since for IPv4 and IPv6, proto
diff --git a/src/api/api_lib.c b/src/api/api_lib.c
index 2735b95f..06bcc8df 100644
--- a/src/api/api_lib.c
+++ b/src/api/api_lib.c
@@ -218,9 +218,9 @@ netconn *netconn_new_with_proto_and_callback(enum netconn_type t, u8_t proto,
 #endif /* LWIP_SO_RCVTIMEO */
 
   msg.function = do_newconn;
-  msg.msg.msg.raw_proto = proto;
+  msg.msg.msg.n.proto = proto;
   msg.msg.conn = conn;
-  tcpip_apimsg(&msg);  
+  tcpip_apimsg(&msg);
 
   if ( conn->err != ERR_OK ) {
     sys_sem_free(conn->sem);
@@ -520,9 +520,9 @@ netconn_recv(struct netconn *conn)
     msg.function = do_recv;
     msg.msg.conn = conn;
     if (buf != NULL) {
-      msg.msg.msg.len = buf->p->tot_len;
+      msg.msg.msg.r.len = buf->p->tot_len;
     } else {
-      msg.msg.msg.len = 1;
+      msg.msg.msg.r.len = 1;
     }
     tcpip_apimsg(&msg);
 #endif /* LWIP_TCP */
@@ -663,10 +663,9 @@ err_t
 netconn_join_leave_group (struct netconn *conn,
                           struct ip_addr *multiaddr,
                           struct ip_addr *interface,
-                          u16_t join_or_leave)
+                          enum netconn_igmp join_or_leave)
 {
   struct api_msg msg;
-  struct ip_addr *ipaddr[2];
 
   if (conn == NULL) {
     return ERR_VAL;
@@ -676,13 +675,11 @@ netconn_join_leave_group (struct netconn *conn,
     return conn->err;
   }
 
-  ipaddr[0] = multiaddr;
-  ipaddr[1] = interface;
-
   msg.function = do_join_leave_group;
   msg.msg.conn = conn;
-  msg.msg.msg.bc.ipaddr = (struct ip_addr *)ipaddr;
-  msg.msg.msg.bc.port = join_or_leave; /* misusing the port field */
+  msg.msg.msg.jl.multiaddr = multiaddr;
+  msg.msg.msg.jl.interface = interface;
+  msg.msg.msg.jl.join_or_leave = join_or_leave;
   tcpip_apimsg(&msg);
   return conn->err;
 }
diff --git a/src/api/api_msg.c b/src/api/api_msg.c
index c50c7972..e1e08922 100644
--- a/src/api/api_msg.c
+++ b/src/api/api_msg.c
@@ -293,52 +293,54 @@ pcb_new(struct api_msg_msg *msg)
    switch(msg->conn->type) {
 #if LWIP_RAW
    case NETCONN_RAW:
-      msg->conn->pcb.raw = raw_new(msg->msg.raw_proto);
-      if(msg->conn->pcb.raw == NULL) {
-        msg->conn->err = ERR_MEM;
-        break;
-      }
-      raw_recv(msg->conn->pcb.raw, recv_raw, msg->conn);
-      break;
+     msg->conn->pcb.raw = raw_new(msg->msg.n.proto);
+     if(msg->conn->pcb.raw == NULL) {
+       msg->conn->err = ERR_MEM;
+       break;
+     }
+     raw_recv(msg->conn->pcb.raw, recv_raw, msg->conn);
+     break;
 #endif /* LWIP_RAW */
 #if LWIP_UDP
    case NETCONN_UDPLITE:
-      msg->conn->pcb.udp = udp_new();
-      if(msg->conn->pcb.udp == NULL) {
-        msg->conn->err = ERR_MEM;
-        break;
-      }
-      udp_setflags(msg->conn->pcb.udp, UDP_FLAGS_UDPLITE);
-      udp_recv(msg->conn->pcb.udp, recv_udp, msg->conn);
-      break;
+     msg->conn->pcb.udp = udp_new();
+     if(msg->conn->pcb.udp == NULL) {
+       msg->conn->err = ERR_MEM;
+       break;
+     }
+     udp_setflags(msg->conn->pcb.udp, UDP_FLAGS_UDPLITE);
+     udp_recv(msg->conn->pcb.udp, recv_udp, msg->conn);
+     break;
    case NETCONN_UDPNOCHKSUM:
-      msg->conn->pcb.udp = udp_new();
-      if(msg->conn->pcb.udp == NULL) {
-        msg->conn->err = ERR_MEM;
-        break;
-      }
-      udp_setflags(msg->conn->pcb.udp, UDP_FLAGS_NOCHKSUM);
-      udp_recv(msg->conn->pcb.udp, recv_udp, msg->conn);
-      break;
+     msg->conn->pcb.udp = udp_new();
+     if(msg->conn->pcb.udp == NULL) {
+       msg->conn->err = ERR_MEM;
+       break;
+     }
+     udp_setflags(msg->conn->pcb.udp, UDP_FLAGS_NOCHKSUM);
+     udp_recv(msg->conn->pcb.udp, recv_udp, msg->conn);
+     break;
    case NETCONN_UDP:
-      msg->conn->pcb.udp = udp_new();
-      if(msg->conn->pcb.udp == NULL) {
-        msg->conn->err = ERR_MEM;
-        break;
-      }
-      udp_recv(msg->conn->pcb.udp, recv_udp, msg->conn);
-      break;
+     msg->conn->pcb.udp = udp_new();
+     if(msg->conn->pcb.udp == NULL) {
+       msg->conn->err = ERR_MEM;
+       break;
+     }
+     udp_recv(msg->conn->pcb.udp, recv_udp, msg->conn);
+     break;
 #endif /* LWIP_UDP */
 #if LWIP_TCP
    case NETCONN_TCP:
-      msg->conn->pcb.tcp = tcp_new();
-      if(msg->conn->pcb.tcp == NULL) {
-        msg->conn->err = ERR_MEM;
-        break;
-      }
-      setup_tcp(msg->conn);
-      break;
+     msg->conn->pcb.tcp = tcp_new();
+     if(msg->conn->pcb.tcp == NULL) {
+       msg->conn->err = ERR_MEM;
+       break;
+     }
+     setup_tcp(msg->conn);
+     break;
 #endif /* LWIP_TCP */
+   default:
+     break;
    }
 
   return msg->conn->err;
@@ -391,9 +393,10 @@ do_delconn(struct api_msg_msg *msg)
           tcp_abort(msg->conn->pcb.tcp);
         }
       }
+      break;
 #endif /* LWIP_TCP */
     default:
-    break;
+      break;
     }
   }
   /* Trigger select() in socket layer */
@@ -432,6 +435,7 @@ do_bind(struct api_msg_msg *msg)
 #if LWIP_TCP
       case NETCONN_TCP:
         msg->conn->err = tcp_bind(msg->conn->pcb.tcp, msg->msg.bc.ipaddr, msg->msg.bc.port);
+        break;
 #endif /* LWIP_TCP */
       default:
         break;
@@ -496,8 +500,8 @@ do_connect(struct api_msg_msg *msg)
     setup_tcp(msg->conn);
     msg->conn->err = tcp_connect(msg->conn->pcb.tcp, msg->msg.bc.ipaddr, msg->msg.bc.port,
     do_connected);
+    break;
 #endif /* LWIP_TCP */
-
   default:
     break;
   }
@@ -558,7 +562,7 @@ do_send(struct api_msg_msg *msg)
       switch (msg->conn->type) {
 #if LWIP_RAW
       case NETCONN_RAW:
-        if (msg->msg.b->addr==NULL) {
+        if (msg->msg.b->addr == NULL) {
           msg->conn->err = raw_send(msg->conn->pcb.raw, msg->msg.b->p);
         } else {
           msg->conn->err = raw_sendto(msg->conn->pcb.raw, msg->msg.b->p, msg->msg.b->addr);
@@ -569,15 +573,14 @@ do_send(struct api_msg_msg *msg)
       case NETCONN_UDPLITE:
       case NETCONN_UDPNOCHKSUM:
       case NETCONN_UDP:
-        if (msg->msg.b->addr==NULL) {
+        if (msg->msg.b->addr == NULL) {
           msg->conn->err = udp_send(msg->conn->pcb.udp, msg->msg.b->p);
         } else {
           msg->conn->err = udp_sendto(msg->conn->pcb.udp, msg->msg.b->p, msg->msg.b->addr, msg->msg.b->port);
         }
         break;
 #endif /* LWIP_UDP */
-      case NETCONN_TCP:
-        /* nothing to do */
+      default:
         break;
       }
     }
@@ -592,7 +595,7 @@ do_recv(struct api_msg_msg *msg)
   if (msg->conn->err == ERR_OK) {
     if (msg->conn->pcb.tcp != NULL) {
       if (msg->conn->type == NETCONN_TCP) {
-        tcp_recved(msg->conn->pcb.tcp, msg->msg.len);
+        tcp_recved(msg->conn->pcb.tcp, msg->msg.r.len);
       }
     }
   }
@@ -609,7 +612,7 @@ do_write(struct api_msg_msg *msg)
   if (msg->conn->err == ERR_OK) {
     if (msg->conn->pcb.tcp != NULL) {
       if (msg->conn->type == NETCONN_TCP) {
-#if LWIP_TCP 
+#if LWIP_TCP
         err = tcp_write(msg->conn->pcb.tcp, msg->msg.w.dataptr,
                         msg->msg.w.len, msg->msg.w.copy);
         /* This is the Nagle algorithm: inhibit the sending of new TCP
@@ -666,9 +669,10 @@ do_join_leave_group(struct api_msg_msg *msg)
       case NETCONN_UDPLITE:
       case NETCONN_UDPNOCHKSUM:
       case NETCONN_UDP:
-        switch(msg->msg.bc.port){ /* misusing the port field */
-          case NETCONN_JOIN:  msg->conn->err = igmp_joingroup (netif_default, ((struct ip_addr**)(msg->msg.bc.ipaddr))[0]); break;
-          case NETCONN_LEAVE: msg->conn->err = igmp_leavegroup(netif_default, ((struct ip_addr**)(msg->msg.bc.ipaddr))[0]); break;
+        if (msg->msg.jl.join_or_leave == NETCONN_JOIN) {
+          msg->conn->err = igmp_joingroup ( netif_default, msg->msg.jl.multiaddr);
+        } else {
+          msg->conn->err = igmp_leavegroup( netif_default, msg->msg.jl.multiaddr);
         }
         break;
 #endif /* LWIP_UDP */
diff --git a/src/include/lwip/api.h b/src/include/lwip/api.h
index aa0d4b00..03685027 100644
--- a/src/include/lwip/api.h
+++ b/src/include/lwip/api.h
@@ -176,7 +176,7 @@ err_t             netconn_close   (struct netconn *conn);
 err_t             netconn_join_leave_group (struct netconn *conn,
                                             struct ip_addr *multiaddr,
                                             struct ip_addr *interface,
-                                            u16_t join_or_leave);
+                                            enum netconn_igmp join_or_leave);
 #endif /* LWIP_IGMP */
 
 err_t             netconn_err     (struct netconn *conn);
diff --git a/src/include/lwip/api_msg.h b/src/include/lwip/api_msg.h
index 999f457b..dc9bc55b 100644
--- a/src/include/lwip/api_msg.h
+++ b/src/include/lwip/api_msg.h
@@ -54,19 +54,29 @@ struct api_msg_msg {
   struct netconn *conn;
   enum netconn_type conntype;
   union {
-    struct pbuf *p;
-    struct netbuf *b;
-    struct  {
+    struct netbuf *b; /* do_send */
+    struct {
+      u8_t proto;
+    } n; /* do_newconn */
+    struct {
       struct ip_addr *ipaddr;
       u16_t port;
-    } bc; /* do_newconn, do_bind, do_connect, do_join_leave_group*/
+    } bc; /* do_bind, do_connect */
     struct {
       const void *dataptr;
       u16_t len;
       u8_t copy;
     } w; /* do_write */
-    u16_t len; /* do_recv */
-    u8_t raw_proto; /* do_newconn */
+    struct {
+      u16_t len;
+    } r; /* do_recv */
+#if LWIP_IGMP
+    struct {
+      struct ip_addr *multiaddr;
+      struct ip_addr *interface;
+      enum netconn_igmp join_or_leave;
+    } jl; /* do_join_leave_group */
+#endif /* LWIP_IGMP */
   } msg;
 };