diff --git a/src/allmydata/test/test_system.py b/src/allmydata/test/test_system.py
index 73d06d552..a18026699 100644
--- a/src/allmydata/test/test_system.py
+++ b/src/allmydata/test/test_system.py
@@ -2,6 +2,7 @@ from __future__ import print_function
 
 import os, re, sys, time, json
 from functools import partial
+from unittest import skipIf
 
 from bs4 import BeautifulSoup
 
@@ -654,6 +655,7 @@ def _render_section_values(values):
 
 class SystemTestMixin(pollmixin.PollMixin, testutil.StallMixin):
 
+    @skipIf(os.environ.get("SKIP_TEST_SYSTEM"), "SKIP_TEST_SYSTEM was set.")
     def setUp(self):
         self.port_assigner = SameProcessStreamEndpointAssigner()
         self.port_assigner.setUp()
diff --git a/tox.ini b/tox.ini
index 2cb59388f..c744e3585 100644
--- a/tox.ini
+++ b/tox.ini
@@ -62,7 +62,8 @@ commands =
          # Python 3.x yet.
          !py36: tahoe --version
 
-         !coverage: trial {env:TAHOE_LAFS_TRIAL_ARGS:--rterrors} {posargs:{env:TEST_SUITE}}
+         !coverage: trial {env:TAHOE_LAFS_TRIAL_ARGS:--rterrors} allmydata.test.test_system
+         !coverage: env SKIP_TEST_SYSTEM=1 trial {env:TAHOE_LAFS_TRIAL_ARGS:--rterrors} {posargs:{env:TEST_SUITE}}
 
          # measuring coverage is somewhat slower than not measuring coverage
          # so only do it on request.