diff --git a/tox.ini b/tox.ini
index 81ff6f724..e88cb8a9e 100644
--- a/tox.ini
+++ b/tox.ini
@@ -17,7 +17,9 @@ usedevelop = true
 
 [testenv:unittests]
 # https://bitbucket.org/hpk42/tox/issue/246/ - only needed for Windows though
-setenv = QT_QPA_PLATFORM_PLUGIN_PATH={envdir}/Lib/site-packages/PyQt5/plugins/platforms
+setenv =
+    QT_QPA_PLATFORM_PLUGIN_PATH={envdir}/Lib/site-packages/PyQt5/plugins/platforms
+    PYTEST_QT_API=pyqt5
 passenv = PYTHON DISPLAY XAUTHORITY HOME
 deps =
     -r{toxinidir}/requirements.txt