diff --git a/tox.ini b/tox.ini
index 40974d8..748872a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -16,6 +16,13 @@ deps =
     pytest-cov
     coverage
 extras = test
+# Unfortunately, tox does not allow separate installation flags for the project
+# dependencies and the test dependencies. When running tox, we want to install the
+# project dependencies with the --pre flag, so that we get the latest version of all
+# dependencies. We do the installation step ourselves for this reason.
+skip_install = true
+commands_pre =
+    pip install --pre -e .[test]
 commands =
 # Capturing output will fail on pypy, possibly due to this issue: https://github.com/pytest-dev/pytest/issues/5502
     pytest --basetemp="{envtmpdir}" {posargs:--color=yes --capture=no --cov=flow --cov-report=term-missing -v tests}