diff --git a/tox.ini b/tox.ini
index a21ea99..cc68d31 100644
--- a/tox.ini
+++ b/tox.ini
@@ -6,7 +6,9 @@ skipsdist = True
 [testenv]
 usedevelop = True
 install_command = pip install -U {opts} {packages}
-setenv = VIRTUAL_ENV={envdir}
+setenv =
+  LANG=en_US.utf8
+  VIRTUAL_ENV={envdir}
 
 deps = -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt