diff --git a/tox.ini b/tox.ini
index 717a238..4cb7a27 100644
--- a/tox.ini
+++ b/tox.ini
@@ -7,6 +7,7 @@ skipsdist = True
 usedevelop = True
 setenv = OS_STDOUT_NOCAPTURE=False
          OS_STDERR_NOCAPTURE=False
+         PYTHONDONTWRITEBYTECODE=1
 
 # Nowadays, TOX_CONSTRAINTS_FILE should be used, but some older scripts might
 # still be using UPPER_CONSTRAINTS_FILE, so we check both variables and use the