diff --git a/tox.ini b/tox.ini
index 8d4a6023..0faf31af 100644
--- a/tox.ini
+++ b/tox.ini
@@ -5,7 +5,7 @@ skipsdist = True
 
 [testenv]
 usedevelop = True
-install_command = pip install {opts} {packages}
+install_command = pip install -U {opts} {packages}
 setenv = LANG=en_US.UTF-8
          LANGUAGE=en_US:en
          LC_ALL=C