diff --git a/libvncserver/sockets.c b/libvncserver/sockets.c
index 84c9c98..3ff2aac 100644
--- a/libvncserver/sockets.c
+++ b/libvncserver/sockets.c
@@ -402,9 +402,9 @@ rfbProcessNewConnection(rfbScreenInfoPtr rfbScreen)
       rfbLogPerror("rfbProcessNewConnection: error in select");
       return FALSE;
     }
-    if (FD_ISSET(rfbScreen->listenSock, &listen_fds)) 
+    if (rfbScreen->listenSock >= 0 && FD_ISSET(rfbScreen->listenSock, &listen_fds))
       chosen_listen_sock = rfbScreen->listenSock;
-    if (FD_ISSET(rfbScreen->listen6Sock, &listen_fds)) 
+    if (rfbScreen->listen6Sock >= 0 && FD_ISSET(rfbScreen->listen6Sock, &listen_fds))
       chosen_listen_sock = rfbScreen->listen6Sock;
 
     if ((sock = accept(chosen_listen_sock,