diff --git a/tests/trace/test_dictifiable.py b/tests/trace/test_dictifiable.py
new file mode 100644
index 000000000000..e99ecf29e130
--- /dev/null
+++ b/tests/trace/test_dictifiable.py
@@ -0,0 +1,45 @@
+import weave
+
+
+def test_dictifiable(client):
+    class NonDictifiable:
+        attr: int
+
+        def __init__(self, attr: int):
+            self.attr = attr
+
+    class Dictifiable:
+        attr: int
+
+        def __init__(self, attr: int):
+            self.attr = attr
+
+        def to_dict(self):
+            return {"attr": self.attr}
+
+    @weave.op
+    def func(d: Dictifiable, nd: NonDictifiable) -> dict:
+        return {
+            "d": Dictifiable(d.attr),
+            "nd": NonDictifiable(nd.attr),
+        }
+
+    val = 42
+    d = Dictifiable(val)
+    nd = NonDictifiable(val)
+    res = func(d, nd)
+    assert isinstance(res["d"], Dictifiable)
+    assert res["d"].attr == val
+    assert isinstance(res["nd"], NonDictifiable)
+    assert res["nd"].attr == val
+
+    call = func.calls()[0]
+
+    assert call.inputs["d"] == {"attr": val}
+    assert call.inputs["nd"].startswith(
+        "<test_dictifiable.test_dictifiable.<locals>.NonDictifiable object at"
+    )
+    assert call.output["d"] == {"attr": val}
+    assert call.output["nd"].startswith(
+        "<test_dictifiable.test_dictifiable.<locals>.NonDictifiable object at"
+    )