diff --git a/testing/marionette/client/marionette_driver/transport.py b/testing/marionette/client/marionette_driver/transport.py
index 97dcdee1c6fd..679b14562fd7 100644
--- a/testing/marionette/client/marionette_driver/transport.py
+++ b/testing/marionette/client/marionette_driver/transport.py
@@ -305,8 +305,10 @@ class TcpTransport(object):
                 if exc.errno not in (57, 107):
                     raise
 
-            self._sock.close()
-            self._sock = None
+            if self._sock:
+                # Guard against unclean shutdown.
+                self._sock.close()
+                self._sock = None
 
     def __del__(self):
         self.close()