diff --git a/misc/build_helpers/run-deprecations.py b/misc/build_helpers/run-deprecations.py
index 3972d5c89..f99cf90aa 100644
--- a/misc/build_helpers/run-deprecations.py
+++ b/misc/build_helpers/run-deprecations.py
@@ -20,7 +20,7 @@ class Options(usage.Options):
         self["args"] = list(args)
 
     description = """Run as:
-PYTHONWARNINGS=default::DeprecationWarning python run-deprecations.py [--warnings=STDERRFILE] [--package=PYTHONPACKAGE ] COMMAND ARGS..
+python run-deprecations.py [--warnings=STDERRFILE] [--package=PYTHONPACKAGE ] COMMAND ARGS..
 """
 
 class RunPP(protocol.ProcessProtocol):
@@ -79,12 +79,6 @@ def run_command(main):
                              (command, os.environ.get("PATH")))
         exe = executables[0]
 
-    pw = os.environ.get("PYTHONWARNINGS")
-    DDW = "default::DeprecationWarning"
-    if pw != DDW:
-        print("note: $PYTHONWARNINGS is '%s', not the expected %s" % (pw, DDW))
-        sys.stdout.flush()
-
     pp = RunPP()
     pp.d = defer.Deferred()
     pp.stdout = io.BytesIO()
diff --git a/tox.ini b/tox.ini
index 97ad3883a..2826f0d62 100644
--- a/tox.ini
+++ b/tox.ini
@@ -168,14 +168,10 @@ commands =
          git commit -m "update NEWS.txt for release"
 
 [testenv:deprecations]
-setenv =
-         PYTHONWARNINGS=default::DeprecationWarning
 commands =
          python misc/build_helpers/run-deprecations.py --package allmydata --warnings={env:TAHOE_LAFS_WARNINGS_LOG:_trial_temp/deprecation-warnings.log} trial {env:TAHOE_LAFS_TRIAL_ARGS:--rterrors} {posargs:allmydata}
 
 [testenv:upcoming-deprecations]
-setenv =
-         PYTHONWARNINGS=default::DeprecationWarning
 deps =
      # Take the base deps as well!
      {[testenv]deps}