diff --git a/src/brush/estimator.py b/src/brush/estimator.py
index 03553645..b9de73e4 100644
--- a/src/brush/estimator.py
+++ b/src/brush/estimator.py
@@ -403,7 +403,7 @@ def _make_data(self, X, y=None, feature_names=[], validation_size=0.0):
         
         assert isinstance(X, np.ndarray)
 
-        if isinstance(y, None):
+        if y is None:
             return _brush.Dataset(X=X,
                     feature_names=feature_names, validation_size=validation_size)