diff --git a/mplaltair/_data.py b/mplaltair/_data.py
index 55dc6bc..ade8a35 100644
--- a/mplaltair/_data.py
+++ b/mplaltair/_data.py
@@ -34,6 +34,12 @@ def _normalize_data(chart):
         df = pd.DataFrame(_fetch(spec['data']['url']))
     elif spec['data'].get('values'):
         return
+    elif spec['data'].get('name'):
+        datasets = spec.get('datasets', {})
+        if spec['data'].get('name') in datasets.keys():
+            return
+        else:
+            raise ValidationError('Named Data is provided but no corresponding dataset is found')
     else:
         raise NotImplementedError('Given data specification is unsupported at the moment.')
 
diff --git a/mplaltair/tests/test_data.py b/mplaltair/tests/test_data.py
index 0f4871d..3674b93 100644
--- a/mplaltair/tests/test_data.py
+++ b/mplaltair/tests/test_data.py
@@ -2,6 +2,7 @@
 import pandas as pd
 import matplotlib.dates as mdates
 import mplaltair._data as _data
+from mplaltair._exceptions import ValidationError
 import pytest
 from vega_datasets import data
 
@@ -26,6 +27,11 @@ def test_data_url():
     _data._normalize_data(chart)
     assert type(chart.data) == pd.DataFrame
 
+def test_named_data():
+    chart = alt.Chart(alt.NamedData('test-dataset')).mark_point()
+    with pytest.raises(ValidationError):
+        _data._normalize_data(chart)
+
 # test date conversion:
 
 df_nonstandard = pd.DataFrame({