diff --git a/requirements-dev.txt b/requirements-dev.txt
index 8341bcbdb2..ebd11f7ecc 100644
--- a/requirements-dev.txt
+++ b/requirements-dev.txt
@@ -1,6 +1,6 @@
 -r requirements.txt
 -r requirements-optional.txt
-pytest>=3.5.0
+pytest>=3.2.5
 mock>=2.0.0
 flake8
 protobuf
diff --git a/requirements-optional.txt b/requirements-optional.txt
index a938405673..6280c354a9 100644
--- a/requirements-optional.txt
+++ b/requirements-optional.txt
@@ -1,3 +1,4 @@
 hidapi >= 0.7.99.post20
-rlp >= 0.4.4
+rlp == 0.4.4; python_version < '3.5'
+rlp >= 0.4.4; python_version >= '3.5'
 ethjsonrpc >= 0.3.0
diff --git a/tox.ini b/tox.ini
index a60d278054..555a08680d 100644
--- a/tox.ini
+++ b/tox.ini
@@ -9,6 +9,14 @@ envlist =
 deps =
     -rrequirements-dev.txt
 commands =
+    # Generate local files
+    python setup.py prebuild
+    # Working in the local directory, try to compile all bytecode
     python -m compileall trezorlib/
-    python trezorctl --help
+    # From installed version, smoke-test trezorctl
+    trezorctl --help
+    # Run non-device-dependent tests
     python -m pytest --pyarg trezorlib.tests.unit_tests
+    # This whole thing is a hack, as the tests run against the cwd version of
+    # python-trezor, as opposed to what is installed.
+    # A better solution would be to put `trezorlib` into `src`. But that's not done yet