diff --git a/tox.ini b/tox.ini
index ffb3b0e5..2275ee28 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,6 +9,7 @@ usedevelop = True
 install_command = pip install -U --force-reinstall {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
+   PYTHONWARNINGS=default::DeprecationWarning
    TRICIRCLE_TEST_DIRECTORY=tricircle/tests
 deps =
     -r{toxinidir}/test-requirements.txt