diff --git a/CHANGELOG b/CHANGELOG
index 9408a17e..5a843a86 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -166,6 +166,11 @@ HISTORY
 
   ++ Bug fixes:
 
+  2007-05-23 Frédéric Bernon
+  * api_lib.c: Fixed bug #5957 "Safe-thread problem inside netconn_recv" to return
+    an error code if it's impossible to fetch a pbuf on a TCP connection (and not
+    directly close the recvmbox).
+
   2007-05-22 Simon Goldschmidt
   * tcp.c: Fixed bug #1895 (tcp_bind not correct) by introducing a list of
     bound but unconnected (and non-listening) tcp_pcbs.
diff --git a/src/api/api_lib.c b/src/api/api_lib.c
index f7633ca1..cc032238 100644
--- a/src/api/api_lib.c
+++ b/src/api/api_lib.c
@@ -496,12 +496,10 @@ netconn_recv(struct netconn *conn)
     if (conn->callback)
       (*conn->callback)(conn, NETCONN_EVT_RCVMINUS, len);
 
-    /* If we are closed, we indicate that we no longer wish to receive
-       data by setting conn->recvmbox to SYS_MBOX_NULL. */
+    /* If we are closed, we indicate that we no longer wish to use the socket */
     if (p == NULL) {
       memp_free(MEMP_NETBUF, buf);
-      sys_mbox_free(conn->recvmbox);
-      conn->recvmbox = SYS_MBOX_NULL;
+      conn->err = ERR_CLSD;
       return NULL;
     }