diff --git a/src/a2a/utils/proto_utils.py b/src/a2a/utils/proto_utils.py
index 14ac098d2..57272c89e 100644
--- a/src/a2a/utils/proto_utils.py
+++ b/src/a2a/utils/proto_utils.py
@@ -230,6 +230,8 @@ def task_state(cls, state: types.TaskState) -> a2a_pb2.TaskState:
                 return a2a_pb2.TaskState.TASK_STATE_INPUT_REQUIRED
             case types.TaskState.auth_required:
                 return a2a_pb2.TaskState.TASK_STATE_AUTH_REQUIRED
+            case types.TaskState.rejected:
+                return a2a_pb2.TaskState.TASK_STATE_REJECTED
             case _:
                 return a2a_pb2.TaskState.TASK_STATE_UNSPECIFIED
 
@@ -703,6 +705,8 @@ def task_state(cls, state: a2a_pb2.TaskState) -> types.TaskState:
                 return types.TaskState.input_required
             case a2a_pb2.TaskState.TASK_STATE_AUTH_REQUIRED:
                 return types.TaskState.auth_required
+            case a2a_pb2.TaskState.TASK_STATE_REJECTED:
+                return types.TaskState.rejected
             case _:
                 return types.TaskState.unknown
 
diff --git a/tests/server/apps/rest/test_rest_fastapi_app.py b/tests/server/apps/rest/test_rest_fastapi_app.py
index 3010c3a56..9ea8c9686 100644
--- a/tests/server/apps/rest/test_rest_fastapi_app.py
+++ b/tests/server/apps/rest/test_rest_fastapi_app.py
@@ -352,5 +352,52 @@ async def mock_stream_response():
     assert response.status_code == 200
 
 
+@pytest.mark.anyio
+async def test_send_message_rejected_task(
+    client: AsyncClient, request_handler: MagicMock
+) -> None:
+    expected_response = a2a_pb2.SendMessageResponse(
+        task=a2a_pb2.Task(
+            id='test_task_id',
+            context_id='test_context_id',
+            status=a2a_pb2.TaskStatus(
+                state=a2a_pb2.TaskState.TASK_STATE_REJECTED,
+                update=a2a_pb2.Message(
+                    message_id='test',
+                    role=a2a_pb2.ROLE_AGENT,
+                    content=[
+                        a2a_pb2.Part(text="I don't want to work"),
+                    ],
+                ),
+            ),
+        ),
+    )
+    request_handler.on_message_send.return_value = Task(
+        id='test_task_id',
+        context_id='test_context_id',
+        status=TaskStatus(
+            state=TaskState.rejected,
+            message=Message(
+                message_id='test',
+                role=Role.agent,
+                parts=[Part(TextPart(text="I don't want to work"))],
+            ),
+        ),
+    )
+    request = a2a_pb2.SendMessageRequest(
+        request=a2a_pb2.Message(),
+        configuration=a2a_pb2.SendMessageConfiguration(),
+    )
+
+    response = await client.post(
+        '/v1/message:send', json=json_format.MessageToDict(request)
+    )
+
+    response.raise_for_status()
+    actual_response = a2a_pb2.SendMessageResponse()
+    json_format.Parse(response.text, actual_response)
+    assert expected_response == actual_response
+
+
 if __name__ == '__main__':
     pytest.main([__file__])
diff --git a/tests/utils/test_proto_utils.py b/tests/utils/test_proto_utils.py
index f68d5c100..7fc82aad7 100644
--- a/tests/utils/test_proto_utils.py
+++ b/tests/utils/test_proto_utils.py
@@ -183,9 +183,8 @@ def test_enum_conversions(self):
         )
 
         for state in types.TaskState:
-            if state not in (types.TaskState.unknown, types.TaskState.rejected):
-                proto_state = proto_utils.ToProto.task_state(state)
-                assert proto_utils.FromProto.task_state(proto_state) == state
+            proto_state = proto_utils.ToProto.task_state(state)
+            assert proto_utils.FromProto.task_state(proto_state) == state
 
         # Test unknown state case
         assert (