diff --git a/CHANGELOG b/CHANGELOG
index 7cff4a7b..bee66bb7 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -50,6 +50,9 @@ HISTORY
 
   ++ Bugfixes:
 
+  2010-01-19: Simon Goldschmidt
+  * api_msg.c: Fixed bug #27316: netconn: Possible deadlock in err_tcp
+
   2010-01-18: Iordan Neshev/Simon Goldschmidt
   * src/netif/ppp: reorganised PPP sourcecode to 2.3.11 including some
     bugfix backports from 2.4.x.
diff --git a/src/api/api_msg.c b/src/api/api_msg.c
index 1ceb308e..8dfd34e6 100644
--- a/src/api/api_msg.c
+++ b/src/api/api_msg.c
@@ -312,14 +312,17 @@ err_tcp(void *arg, err_t err)
 {
   struct netconn *conn;
   enum netconn_state old_state;
+  SYS_ARCH_DECL_PROTECT(lev);
 
   conn = arg;
   LWIP_ASSERT("conn != NULL", (conn != NULL));
 
   conn->pcb.tcp = NULL;
 
-  /* no protection since this is always fatal */
+  /* no check since this is always fatal */
+  SYS_ARCH_PROTECT(lev);
   conn->last_err = err;
+  SYS_ARCH_UNPROTECT(lev);
 
   /* API_EVENT might call tcp_tmr, so reset conn->state now */
   old_state = conn->state;
@@ -328,12 +331,14 @@ err_tcp(void *arg, err_t err)
   if (conn->recvmbox != SYS_MBOX_NULL) {
     /* Register event with callback */
     API_EVENT(conn, NETCONN_EVT_RCVPLUS, 0);
-    sys_mbox_post(conn->recvmbox, NULL);
+    /* use trypot to preven deadlock */
+    sys_mbox_trypost(conn->recvmbox, NULL);
   }
   if (conn->acceptmbox != SYS_MBOX_NULL) {
     /* Register event with callback */
     API_EVENT(conn, NETCONN_EVT_RCVPLUS, 0);
-    sys_mbox_post(conn->acceptmbox, NULL);
+    /* use trypot to preven deadlock */
+    sys_mbox_trypost(conn->acceptmbox, NULL);
   }
   if ((old_state == NETCONN_WRITE) || (old_state == NETCONN_CLOSE) ||
       (old_state == NETCONN_CONNECT)) {