diff --git a/lenskit/util/__init__.py b/lenskit/util/__init__.py
index 0ebe9619e..03a4d2333 100644
--- a/lenskit/util/__init__.py
+++ b/lenskit/util/__init__.py
@@ -60,8 +60,10 @@ def clone(algo):
 
         sps = dict([(k, clone(v)) for (k, v) in params.items()])
         return algo.__class__(**sps)
-    elif isinstance(algo, list) or isinstance(algo, tuple):
+    elif isinstance(algo, list):
         return [clone(a) for a in algo]
+    elif isinstance(algo, tuple):
+        return tuple(clone(a) for a in algo)
     else:
         return deepcopy(algo)
 
diff --git a/tests/test_bias.py b/tests/test_bias.py
index 50af8106a..cde6084f4 100644
--- a/tests/test_bias.py
+++ b/tests/test_bias.py
@@ -69,6 +69,22 @@ def test_bias_clone():
     assert getattr(a2, "user_offsets_", None) is None
 
 
+def test_bias_clone_damping():
+    algo = Bias(damping=(10, 5))
+    algo.fit(simple_df)
+
+    params = algo.get_params()
+    assert sorted(params.keys()) == ["damping", "items", "users"]
+
+    a2 = lku.clone(algo)
+    assert a2 is not algo
+    assert getattr(a2, "item_damping", None) == 5
+    assert getattr(a2, "user_damping", None) == 10
+    assert getattr(a2, "mean_", None) is None
+    assert getattr(a2, "item_offsets_", None) is None
+    assert getattr(a2, "user_offsets_", None) is None
+
+
 def test_bias_global_only():
     algo = Bias(users=False, items=False)
     algo.fit(simple_df)
diff --git a/tests/test_util.py b/tests/test_util.py
index 18bf34630..34d408998 100644
--- a/tests/test_util.py
+++ b/tests/test_util.py
@@ -4,12 +4,11 @@
 # Licensed under the MIT license, see LICENSE.md for details.
 # SPDX-License-Identifier: MIT
 
-import time
 import re
-import pathlib
+import time
 
-import numpy as np
-import pandas as pd
+from hypothesis import HealthCheck, given, settings
+from hypothesis import strategies as st
 
 from lenskit import util as lku
 
@@ -50,6 +49,7 @@ def test_stopwatch_long_str():
 def test_stopwatch_minutes():
     w = lku.Stopwatch()
     w.stop()
+    assert w.stop_time is not None
     w.start_time = w.stop_time - 62
     s = str(w)
     p = re.compile(r"1m2.\d\ds")
@@ -59,6 +59,7 @@ def test_stopwatch_minutes():
 def test_stopwatch_hours():
     w = lku.Stopwatch()
     w.stop()
+    assert w.stop_time is not None
     w.start_time = w.stop_time - 3663
     s = str(w)
     p = re.compile(r"1h1m3.\d\ds")
@@ -80,3 +81,23 @@ def func(foo):
     assert len(history) == 1
     cache("bar")
     assert len(history) == 2
+
+
+@settings(suppress_health_check=[HealthCheck.too_slow])
+@given(
+    st.one_of(
+        st.integers(),
+        st.floats(allow_nan=False),
+        st.lists(st.floats(allow_nan=False), max_size=100),
+        st.tuples(st.floats(allow_nan=False)),
+        st.tuples(st.floats(allow_nan=False), st.floats(allow_nan=False)),
+        st.tuples(
+            st.floats(allow_nan=False), st.floats(allow_nan=False), st.floats(allow_nan=False)
+        ),
+        st.emails(),
+    )
+)
+def test_clone_core_obj(obj):
+    o2 = lku.clone(obj)
+    assert o2 == obj
+    assert type(o2) == type(obj)