diff --git a/net/tap-linux.c b/net/tap-linux.c
index f7aa9041b8..ff8cad0ea0 100644
--- a/net/tap-linux.c
+++ b/net/tap-linux.c
@@ -82,12 +82,17 @@ int tap_open(char *ifname, int ifname_size, int *vnet_hdr, int vnet_hdr_required
     return fd;
 }
 
-/* sndbuf should be set to a value lower than the tx queue
- * capacity of any destination network interface.
+/* sndbuf implements a kind of flow control for tap.
+ * Unfortunately when it's enabled, and packets are sent
+ * to other guests on the same host, the receiver
+ * can lock up the transmitter indefinitely.
+ *
+ * To avoid packet loss, sndbuf should be set to a value lower than the tx
+ * queue capacity of any destination network interface.
  * Ethernet NICs generally have txqueuelen=1000, so 1Mb is
- * a good default, given a 1500 byte MTU.
+ * a good value, given a 1500 byte MTU.
  */
-#define TAP_DEFAULT_SNDBUF 1024*1024
+#define TAP_DEFAULT_SNDBUF 0
 
 int tap_set_sndbuf(int fd, QemuOpts *opts)
 {
diff --git a/qemu-options.hx b/qemu-options.hx
index 939297a1b0..598a1bdf77 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1057,7 +1057,7 @@ DEF("net", HAS_ARG, QEMU_OPTION_net,
     "                use '[down]script=no' to disable script execution\n"
     "                use 'fd=h' to connect to an already opened TAP interface\n"
     "                use 'sndbuf=nbytes' to limit the size of the send buffer (the\n"
-    "                default of 'sndbuf=1048576' can be disabled using 'sndbuf=0')\n"
+    "                default is disabled 'sndbuf=0' to enable flow control set 'sndbuf=1048576')\n"
     "                use vnet_hdr=off to avoid enabling the IFF_VNET_HDR tap flag\n"
     "                use vnet_hdr=on to make the lack of IFF_VNET_HDR support an error condition\n"
     "                use vhost=on to enable experimental in kernel accelerator\n"