diff --git a/tox.ini b/tox.ini
index 23ee0026..a86fba4f 100644
--- a/tox.ini
+++ b/tox.ini
@@ -23,7 +23,8 @@ deps =
     # installation (see `skipsdist`), to get relative paths in coverage reports
     --editable {toxinidir}
 
-install_command = pip install --pre {opts} {packages}
+# FIXME: use legacy resolver because https://github.com/pypa/pip/issues/9215
+install_command = pip install --use-deprecated=legacy-resolver --pre {opts} {packages}
 
 
 # Develop test env to run tests against securesystemslib's master branch