diff --git a/labtech/serialization.py b/labtech/serialization.py
index bdb94bd..ee8742d 100644
--- a/labtech/serialization.py
+++ b/labtech/serialization.py
@@ -122,6 +122,16 @@ def deserialize_enum(self, serialized: dict[str, jsonable]) -> Enum:
         return enum_cls[name]
 
     def serialize_class(self, cls: type) -> jsonable:
+        if '<locals>' in cls.__qualname__:
+            raise SerializationError(
+                (f'Unable to serialize class "{cls.__qualname__}" because it was defined in a function. '
+                 'Please ensure all task and parameter classes are defined at the top-level of a module.')
+            )
+
+        if '>' in cls.__qualname__:
+            # This should never happen, but is here for safety.
+            raise SerializationError('Unexpected ">" in class __qualname__')
+
         # Handle nested classes by splitting class nesting path by ">".
         return f'{cls.__module__}.{cls.__qualname__.replace(".", ">")}'
 
diff --git a/tests/labtech/test_serialization.py b/tests/labtech/test_serialization.py
new file mode 100644
index 0000000..3030add
--- /dev/null
+++ b/tests/labtech/test_serialization.py
@@ -0,0 +1,18 @@
+import pytest
+
+from labtech.exceptions import SerializationError
+from labtech.serialization import Serializer
+
+
+class TestSerializer:
+
+    class TestSerializeClass:
+
+        def test_local_object(self):
+
+            class Example:
+                pass
+
+            serializer = Serializer()
+            with pytest.raises(SerializationError, match=f'Unable to serialize class "{Example.__qualname__}" because it was defined in a function.'):
+                serializer.serialize_class(Example)