diff --git a/wrapper/xgboost.py b/wrapper/xgboost.py
index 7e3fa2dc4..46a229cd6 100644
--- a/wrapper/xgboost.py
+++ b/wrapper/xgboost.py
@@ -935,8 +935,8 @@ class XGBClassifier(XGBModel, XGBClassifier):
                                             base_score, seed)
 
     def fit(self, X, y, sample_weight=None):
-        y_values = list(np.unique(y))
-        self.n_classes_ = len(y_values)
+        self.classes_ = list(np.unique(y))
+        self.n_classes_ = len(self.classes_)
         if self.n_classes_ > 2:
             # Switch to using a multiclass objective in the underlying XGB instance
             self.objective = "multi:softprob"