diff --git a/tox.ini b/tox.ini
index b54a221c..9b42599a 100644
--- a/tox.ini
+++ b/tox.ini
@@ -24,15 +24,13 @@ deps =
     # installation (see `skipsdist`), to get relative paths in coverage reports
     --editable {toxinidir}
 
-# FIXME: use legacy resolver because https://github.com/pypa/pip/issues/9215
-install_command = pip install --use-deprecated=legacy-resolver --pre {opts} {packages}
-
+install_command = pip install --pre {opts} {packages}
 
 # Develop test env to run tests against securesystemslib's master branch
 # Must to be invoked explicitly with, e.g. `tox -e with-sslib-master`
 [testenv:with-sslib-master]
 deps =
-    git+http://github.com/secure-systems-lab/securesystemslib.git@master#egg=securesystemslib
+    git+https://github.com/secure-systems-lab/securesystemslib.git@master#egg=securesystemslib[crypto,pynacl]
     -r{toxinidir}/requirements-test.txt
     --editable {toxinidir}