diff --git a/zircon/system/dev/bluetooth/bt-transport-uart/bt-transport-uart.c b/zircon/system/dev/bluetooth/bt-transport-uart/bt-transport-uart.c
index 3a42e7e..c141ab1 100644
--- a/zircon/system/dev/bluetooth/bt-transport-uart/bt-transport-uart.c
+++ b/zircon/system/dev/bluetooth/bt-transport-uart/bt-transport-uart.c
@@ -191,12 +191,13 @@
 
     buf[0] = HCI_COMMAND;
     length++;
-    serial_write(hci, buf, length);
 
     mtx_lock(&hci->mutex);
     snoop_channel_write_locked(hci, bt_hci_snoop_flags(BT_HCI_SNOOP_TYPE_CMD, false), buf + 1,
                                length - 1);
     mtx_unlock(&hci->mutex);
+
+    serial_write(hci, buf, length);
   }
 
   return;
@@ -221,9 +222,13 @@
 
     buf[0] = HCI_ACL_DATA;
     length++;
-    serial_write(hci, buf, length);
+
+    mtx_lock(&hci->mutex);
     snoop_channel_write_locked(hci, bt_hci_snoop_flags(BT_HCI_SNOOP_TYPE_ACL, false), buf + 1,
                                length - 1);
+    mtx_unlock(&hci->mutex);
+
+    serial_write(hci, buf, length);
   }
 
   return;