diff --git a/onedm/sdf/data.py b/onedm/sdf/data.py
index c3ac55f..fd4fb40 100644
--- a/onedm/sdf/data.py
+++ b/onedm/sdf/data.py
@@ -10,7 +10,7 @@
 import datetime
 from typing import Annotated, Any, Literal, Union
 
-from pydantic import Field, NonNegativeInt
+from pydantic import Field, NonNegativeInt, field_serializer
 from pydantic_core import SchemaValidator, core_schema
 
 from .common import CommonQualities
@@ -26,6 +26,10 @@ class DataQualities(CommonQualities, ABC):
     default: Any | None = None
     choices: dict[str, Data] | None = Field(None, alias="sdfChoice")
 
+    @field_serializer("type")
+    def always_include_type(self, type: str, _):
+        return type
+
     def _get_base_schema(self) -> core_schema.CoreSchema:
         """Implemented by sub-classes."""
         raise NotImplementedError
diff --git a/tests/sdf/test_datatypes.py b/tests/sdf/test_datatypes.py
index 5f5e353..08276b9 100644
--- a/tests/sdf/test_datatypes.py
+++ b/tests/sdf/test_datatypes.py
@@ -55,3 +55,8 @@ def test_object_data(test_model: sdf.SDF):
 
 def test_unknown_data(test_model: sdf.SDF):
     assert isinstance(test_model.data["Unknown"], sdf.AnyData)
+
+
+def test_serialization_exluding_defaults():
+    integer = sdf.IntegerData()
+    assert "type" in integer.model_dump(exclude_defaults=True)