diff --git a/tox.ini b/tox.ini
index 3603ea36a..9efc839b6 100644
--- a/tox.ini
+++ b/tox.ini
@@ -68,6 +68,7 @@ commands =
          pip freeze
          tahoe --version
          coverage run --branch -m twisted.trial {env:TAHOE_LAFS_TRIAL_ARGS:--rterrors --reporter=timing} {posargs:allmydata}
+         coverage combine
          coverage xml
 
 [testenv:codechecks]