diff --git a/tox.ini b/tox.ini
index 81d3fe8cbb..bd82031683 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,6 +9,7 @@ passenv=ZUUL_CACHE_DIR
 install_command = pip install -U {opts} {packages}
 setenv =
    VIRTUAL_ENV={envdir}
+   PYTHONUNBUFFERED=1
 basepython = python3
 deps = -r{toxinidir}/test-requirements.txt
 commands =