diff --git a/crossplane/function/resource.py b/crossplane/function/resource.py
index 322a482..3cc79a9 100644
--- a/crossplane/function/resource.py
+++ b/crossplane/function/resource.py
@@ -38,7 +38,15 @@ def update(r: fnv1.Resource, source: dict | structpb.Struct | pydantic.BaseModel
     """
     match source:
         case pydantic.BaseModel():
-            r.resource.update(source.model_dump(exclude_defaults=True, warnings=False))
+            data = source.model_dump(exclude_defaults=True, warnings=False)
+            # In Pydantic, exclude_defaults=True in model_dump excludes fields
+            # that have their value equal to the default. If a field like
+            # apiVersion is set to its default value 's3.aws.upbound.io/v1beta2'
+            # (and not explicitly provided during initialization), it will be
+            # excluded from the serialized output.
+            data['apiVersion'] = source.apiVersion
+            data['kind'] = source.kind
+            r.resource.update(data)
         case structpb.Struct():
             # TODO(negz): Use struct_to_dict and update to match other semantics?
             r.resource.MergeFrom(source)
diff --git a/tests/test_resource.py b/tests/test_resource.py
index e9c818f..2f9523b 100644
--- a/tests/test_resource.py
+++ b/tests/test_resource.py
@@ -90,7 +90,11 @@ class TestResource(unittest.TestCase):
                 ),
                 want=fnv1.Resource(
                     resource=resource.dict_to_struct(
-                        {"spec": {"forProvider": {"region": "us-west-2"}}}
+                        {
+                            "apiVersion": "s3.aws.upbound.io/v1beta1",
+                            "kind": "Bucket",
+                            "spec": {"forProvider": {"region": "us-west-2"}},
+                        }
                     ),
                 ),
             ),
diff --git a/tests/testdata/models/io/upbound/aws/s3/v1beta2.py b/tests/testdata/models/io/upbound/aws/s3/v1beta2.py
index 0a678e0..d6253ff 100644
--- a/tests/testdata/models/io/upbound/aws/s3/v1beta2.py
+++ b/tests/testdata/models/io/upbound/aws/s3/v1beta2.py
@@ -759,11 +759,11 @@ class Status(BaseModel):
 
 
 class Bucket(BaseModel):
-    apiVersion: Optional[str] = None
+    apiVersion: Optional[str] = 's3.aws.upbound.io/v1beta2'
     """
     APIVersion defines the versioned schema of this representation of an object. Servers should convert recognized schemas to the latest internal value, and may reject unrecognized values. More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#resources
     """
-    kind: Optional[str] = None
+    kind: Optional[str] = 'Bucket'
     """
     Kind is a string value representing the REST resource this object represents. Servers may infer this from the endpoint the client submits requests to. Cannot be updated. In CamelCase. More info: https://git.k8s.io/community/contributors/devel/sig-architecture/api-conventions.md#types-kinds
     """