diff --git a/.circleci/config.yml b/.circleci/config.yml
index f004e6a81..55aacc5ff 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -90,7 +90,7 @@ commands:
     steps:
       - run:
           name: install macOS packages
-          command: HOMEBREW_NO_AUTO_UPDATE=1 brew install coreutils parallel gnu-getopt
+          command: HOMEBREW_NO_AUTO_UPDATE=1 brew install coreutils gnu-getopt parallel python@3.9 virtualenv
 
       - checkout
 
@@ -138,11 +138,13 @@ commands:
       # Download and cache dependencies
       - restore_cache:
           keys:
-            - v11win-dependencies-{{ checksum "setup.py" }}-{{ checksum "ci/build_and_activate_venv.ps1" }}
+            - v13win-dependencies-{{ checksum "setup.py" }}-{{ checksum "ci/build_and_activate_venv.ps1" }}
 
       - run:
           name: install python
-          command: choco install --allow-downgrade -y python --version=3.8.10
+          # Use python3.9 in Windows instead of python3.8 because otherwise
+          # pytest-notebook's indirect dependency pywinpty will fail to build.
+          command: choco install --allow-downgrade -y python --version=3.9.13
           shell: powershell.exe
 
       - run:
@@ -163,14 +165,20 @@ commands:
 
       - run:
           name: install dependencies
-          # Only create venv if it's not been restored from cache
-          command: if (-not (Test-Path venv)) { .\ci\build_and_activate_venv.ps1 -venv venv }
+          # Only create venv if it's not been restored from cache.
+          # Need to throw error explicitly on error or else {} will get rid of
+          # the exit code.
+          command: |
+            if (-not (Test-Path venv)) {
+                .\ci\build_and_activate_venv.ps1 -venv venv
+                if ($LASTEXITCODE -ne 0) { throw "Failed to create venv" }
+            }
           shell: powershell.exe
 
       - save_cache:
           paths:
             - .\venv
-          key: v11win-dependencies-{{ checksum "setup.py" }}-{{ checksum "ci/build_and_activate_venv.ps1" }}
+          key: v13win-dependencies-{{ checksum "setup.py" }}-{{ checksum "ci/build_and_activate_venv.ps1" }}
 
       - run:
           name: install imitation
diff --git a/ci/build_and_activate_venv.ps1 b/ci/build_and_activate_venv.ps1
index 01ad7e375..661e32419 100644
--- a/ci/build_and_activate_venv.ps1
+++ b/ci/build_and_activate_venv.ps1
@@ -7,6 +7,6 @@ If ($venv -eq $null) {
    $venv = "venv"
 }
 
-virtualenv -p python3.8 $venv
+virtualenv -p python3.9 $venv
 & $venv\Scripts\activate
 pip install ".[docs,parallel,test]"
diff --git a/mypy.ini b/mypy.ini
index ec5b4fd3f..3d555eadb 100644
--- a/mypy.ini
+++ b/mypy.ini
@@ -1,3 +1,8 @@
 [mypy]
 ignore_missing_imports = true
 exclude = output
+
+# torch had some type errors, we ignore them because they're not our fault
+[mypy-torch._dynamo.*]
+follow_imports = skip
+follow_imports_for_stubs = True
diff --git a/src/imitation/algorithms/adversarial/common.py b/src/imitation/algorithms/adversarial/common.py
index ece30b011..bde75f83d 100644
--- a/src/imitation/algorithms/adversarial/common.py
+++ b/src/imitation/algorithms/adversarial/common.py
@@ -207,7 +207,7 @@ def __init__(
         self.debug_use_ground_truth = debug_use_ground_truth
         self.venv = venv
         self.gen_algo = gen_algo
-        self._reward_net = reward_net.to(gen_algo.device)
+        self._reward_net: reward_nets.RewardNet = reward_net.to(gen_algo.device)
         self._log_dir = util.parse_path(log_dir)
 
         # Create graph for optimising/recording stats on discriminator
diff --git a/src/imitation/data/serialize.py b/src/imitation/data/serialize.py
index ee9d0d3f8..fe6508cdb 100644
--- a/src/imitation/data/serialize.py
+++ b/src/imitation/data/serialize.py
@@ -20,7 +20,7 @@ def save(path: AnyPath, trajectories: Sequence[Trajectory]) -> None:
         trajectories: The trajectories to save.
     """
     p = util.parse_path(path)
-    huggingface_utils.trajectories_to_dataset(trajectories).save_to_disk(p)
+    huggingface_utils.trajectories_to_dataset(trajectories).save_to_disk(str(p))
     logging.info(f"Dumped demonstrations to {p}.")
 
 
diff --git a/src/imitation/policies/base.py b/src/imitation/policies/base.py
index ba1f550df..c12de74e0 100644
--- a/src/imitation/policies/base.py
+++ b/src/imitation/policies/base.py
@@ -31,7 +31,7 @@ def _predict(
     ):
         np_actions = []
         if isinstance(obs, dict):
-            np_obs = types.DictObs(
+            np_obs: Union[types.DictObs, np.ndarray] = types.DictObs(
                 {k: v.detach().cpu().numpy() for k, v in obs.items()},
             )
         else:
diff --git a/src/imitation/util/util.py b/src/imitation/util/util.py
index 8112ebb57..315003265 100644
--- a/src/imitation/util/util.py
+++ b/src/imitation/util/util.py
@@ -255,10 +255,7 @@ def safe_to_tensor(array: Union[np.ndarray, th.Tensor], **kwargs) -> th.Tensor:
     Returns:
         A PyTorch tensor with the same content as `array`.
     """
-    if isinstance(array, th.Tensor):
-        return array
-
-    if not array.flags.writeable:
+    if isinstance(array, np.ndarray) and not array.flags.writeable:
         array = array.copy()
 
     return th.as_tensor(array, **kwargs)
@@ -476,6 +473,6 @@ def split_in_half(x: int) -> Tuple[int, int]:
 def clear_screen() -> None:
     """Clears the console screen."""
     if os.name == "nt":  # Windows
-        os.system("cls")
+        os.system("cls")  # pragma: no cover
     else:
         os.system("clear")
diff --git a/tests/algorithms/test_sqil.py b/tests/algorithms/test_sqil.py
index 4c6fa1844..8f9fbe56e 100644
--- a/tests/algorithms/test_sqil.py
+++ b/tests/algorithms/test_sqil.py
@@ -247,7 +247,7 @@ def test_sqil_performance_continuous(
     pytestconfig: pytest.Config,
     pendulum_single_venv: vec_env.VecEnv,
     rl_algo_class: Type[off_policy_algorithm.OffPolicyAlgorithm],
-):
+):  # pragma: no cover
     rl_kwargs = dict(
         learning_starts=500,
         learning_rate=0.001,
diff --git a/tests/data/test_huggingface_utils.py b/tests/data/test_huggingface_utils.py
index 643cc12e8..5896ba864 100644
--- a/tests/data/test_huggingface_utils.py
+++ b/tests/data/test_huggingface_utils.py
@@ -63,6 +63,8 @@ def test_save_load_roundtrip(
 
 
 @hypothesis.given(st.data(), h_strats.trajectories_list)
+# the first run sometimes takes longer, so we give it more time
+@hypothesis.settings(deadline=datetime.timedelta(milliseconds=300))
 def test_sliced_access(data: st.DataObject, trajectories: Sequence[types.Trajectory]):
     """Test that slicing a TrajectoryDatasetSequence behaves as expected."""
     # GIVEN
@@ -84,6 +86,8 @@ def test_sliced_access(data: st.DataObject, trajectories: Sequence[types.Traject
 
 
 @hypothesis.given(st.data(), h_strats.trajectory)
+# the first run sometimes takes longer, so we give it more time
+@hypothesis.settings(deadline=datetime.timedelta(milliseconds=300))
 def test_sliced_info_dict_access(
     data: st.DataObject,
     trajectory: types.Trajectory,
diff --git a/tests/util/test_util.py b/tests/util/test_util.py
index ce663d8e0..d0fd67b08 100644
--- a/tests/util/test_util.py
+++ b/tests/util/test_util.py
@@ -103,6 +103,8 @@ def test_safe_to_numpy():
     numpy = util.safe_to_numpy(tensor)
     assert (numpy == tensor.numpy()).all()
     assert util.safe_to_numpy(None) is None
+    with pytest.warns(UserWarning, match=".*performance.*"):
+        util.safe_to_numpy(tensor, warn=True)
 
 
 def test_tensor_iter_norm():