diff --git a/hugr-py/src/hugr/tys.py b/hugr-py/src/hugr/tys.py
index ee07bf626..124beaf20 100644
--- a/hugr-py/src/hugr/tys.py
+++ b/hugr-py/src/hugr/tys.py
@@ -237,15 +237,18 @@ def as_tuple(self) -> Tuple:
     def __repr__(self) -> str:
         return f"Sum({self.variant_rows})"
 
+    def __eq__(self, other: object) -> bool:
+        return isinstance(other, Sum) and self.variant_rows == other.variant_rows
+
     def type_bound(self) -> TypeBound:
         return TypeBound.join(*(t.type_bound() for r in self.variant_rows for t in r))
 
 
-@dataclass()
+@dataclass(eq=False)
 class UnitSum(Sum):
     """Simple :class:`Sum` type with `size` variants of empty rows."""
 
-    size: int
+    size: int = field(compare=False)
 
     def __init__(self, size: int):
         self.size = size
@@ -262,7 +265,7 @@ def __repr__(self) -> str:
         return f"UnitSum({self.size})"
 
 
-@dataclass()
+@dataclass(eq=False)
 class Tuple(Sum):
     """Product type with `tys` elements. Instances of this type correspond to
     :class:`Sum` with a single variant.
diff --git a/hugr-py/tests/test_tys.py b/hugr-py/tests/test_tys.py
new file mode 100644
index 000000000..689234426
--- /dev/null
+++ b/hugr-py/tests/test_tys.py
@@ -0,0 +1,14 @@
+from __future__ import annotations
+
+from hugr.tys import Bool, Qubit, Sum, Tuple, UnitSum
+
+
+def test_sums():
+    assert Sum([[Bool, Qubit]]) == Tuple(Bool, Qubit)
+    assert Tuple(Bool, Qubit) == Sum([[Bool, Qubit]])
+    assert Sum([[Bool, Qubit]]).as_tuple() == Sum([[Bool, Qubit]])
+
+    assert Tuple() == Sum([[]])
+    assert UnitSum(0) == Sum([])
+    assert UnitSum(1) == Tuple()
+    assert UnitSum(4) == Sum([[], [], [], []])