diff --git a/tox.ini b/tox.ini
index f25f7d5d9a..ad6f2737b3 100644
--- a/tox.ini
+++ b/tox.ini
@@ -14,6 +14,8 @@ deps =
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 commands = python setup.py testr --slowest --testr-args='{posargs}'
+setenv =
+  LC_ALL=en_US.UTF-8
 
 [testenv:venv]
 commands = {posargs}