diff --git a/masque/shapes/arc.py b/masque/shapes/arc.py
index 6f948cb..4befb6d 100644
--- a/masque/shapes/arc.py
+++ b/masque/shapes/arc.py
@@ -422,7 +422,7 @@ class Arc(PositionableImpl, Shape):
         rotation %= 2 * pi
         width = self.width
 
-        return ((type(self), radii, norm_angles, width / norm_value),
+        return ((type(self), tuple(radii.tolist()), norm_angles, width / norm_value),
                 (self.offset, scale / norm_value, rotation, False),
                 lambda: Arc(
                     radii=radii * norm_value,
diff --git a/masque/shapes/ellipse.py b/masque/shapes/ellipse.py
index 8e3fd49..985d252 100644
--- a/masque/shapes/ellipse.py
+++ b/masque/shapes/ellipse.py
@@ -206,7 +206,7 @@ class Ellipse(PositionableImpl, Shape):
             radii = self.radii[::-1] / self.radius_y
             scale = self.radius_y
             angle = (self.rotation + pi / 2) % pi
-        return ((type(self), radii),
+        return ((type(self), tuple(radii.tolist())),
                 (self.offset, scale / norm_value, angle, False),
                 lambda: Ellipse(radii=radii * norm_value))
 
diff --git a/masque/test/test_library.py b/masque/test/test_library.py
index 09c258b..6ac8536 100644
--- a/masque/test/test_library.py
+++ b/masque/test/test_library.py
@@ -282,6 +282,28 @@ def test_library_dedup_text_preserves_scale_and_mirror_flag() -> None:
     assert [cast("Text", shape).height for shape in flat.shapes[(1, 0)]] == [10, 10]
 
 
+def test_library_dedup_handles_arc_and_ellipse_labels() -> None:
+    lib = Library()
+    pat = Pattern()
+    pat.shapes[(1, 0)] += [
+        Arc(radii=(10, 20), angles=(0, 1), width=2, offset=(0, 0)),
+        Arc(radii=(10, 20), angles=(0, 1), width=2, offset=(50, 0)),
+        ]
+    pat.shapes[(2, 0)] += [
+        Ellipse(radii=(10, 20), offset=(0, 0)),
+        Ellipse(radii=(10, 20), offset=(50, 0)),
+        ]
+    lib["top"] = pat
+
+    lib.dedup(exclude_types=(), norm_value=1, threshold=2)
+
+    assert len(lib["top"].refs) == 2
+    assert lib["top"].shapes[(1, 0)] == []
+    assert lib["top"].shapes[(2, 0)] == []
+
+    flat = lib.flatten("top")["top"]
+    assert sum(isinstance(shape, Arc) for shape in flat.shapes[(1, 0)]) == 2
+    assert sum(isinstance(shape, Ellipse) for shape in flat.shapes[(2, 0)]) == 2
 
 
 def test_library_dedup_handles_multiple_duplicate_groups() -> None: