diff --git a/src/scanspec/core.py b/src/scanspec/core.py
index 75565f20..d180d547 100644
--- a/src/scanspec/core.py
+++ b/src/scanspec/core.py
@@ -198,8 +198,7 @@ def add_member(self, cls: type):
             # called muliple times for the same member, do no process if it wouldn't
             # change the member list
             return
-        if cls is self._base_class:
-            return
+
         self._members.append(cls)
         union = self._make_union()
         if union:
diff --git a/src/scanspec/regions.py b/src/scanspec/regions.py
index c1ef8e22..2a345c06 100644
--- a/src/scanspec/regions.py
+++ b/src/scanspec/regions.py
@@ -1,8 +1,8 @@
 from __future__ import annotations
 
 from collections.abc import Iterator
-from dataclasses import is_dataclass
-from typing import Generic
+from dataclasses import asdict, is_dataclass
+from typing import Any, Generic, Mapping
 
 import numpy as np
 from pydantic import BaseModel, Field
@@ -66,6 +66,10 @@ def __sub__(self, other) -> DifferenceOf[Axis]:
     def __xor__(self, other) -> SymmetricDifferenceOf[Axis]:
         return if_instance_do(other, Region, lambda o: SymmetricDifferenceOf(self, o))
 
+    def serialize(self) -> Mapping[str, Any]:
+        """Serialize the Region to a dictionary."""
+        return asdict(self)  # type: ignore
+
     @staticmethod
     def deserialize(obj):
         """Deserialize the Region from a dictionary."""
diff --git a/tests/test_serialization.py b/tests/test_serialization.py
index adb5729d..89c2e7d7 100644
--- a/tests/test_serialization.py
+++ b/tests/test_serialization.py
@@ -4,7 +4,7 @@
 import pytest
 from pydantic import ValidationError
 
-from scanspec.regions import Circle, Rectangle, UnionOf
+from scanspec.regions import Circle, Rectangle, Region, UnionOf
 from scanspec.specs import Line, Mask, Spec, Spiral
 
 
@@ -15,6 +15,20 @@ def test_line_serializes() -> None:
     assert Spec.deserialize(serialized) == ob
 
 
+def test_circle_serializes() -> None:
+    ob = Circle("x", "y", x_middle=0, y_middle=1, radius=4)
+    serialized = {
+        "x_axis": "x",
+        "y_axis": "y",
+        "x_middle": 0.0,
+        "y_middle": 1.0,
+        "radius": 4.0,
+        "type": "Circle",
+    }
+    assert ob.serialize() == serialized
+    assert Region.deserialize(serialized) == ob
+
+
 def test_masked_circle_serializes() -> None:
     ob = Mask(Line("x", 0, 1, 4), Circle("x", "y", x_middle=0, y_middle=1, radius=4))
     serialized = {