diff --git a/tox.ini b/tox.ini
index 9417aef7d..bf69c097f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -56,6 +56,7 @@ setenv =
        # Define TEST_SUITE in the environment as an aid to constructing the
        # correct test command below.
        TEST_SUITE = allmydata
+       COLUMNS = 80
 
 commands =
          # As an aid to debugging, dump all of the Python packages and their