diff --git a/toolkit.py b/toolkit.py
index cc479a4cde0d64e856597e4a4d3a9df9ff681da6..3d52a59bac7e6febfa2c761e76fe4fff019b12da 100755
--- a/toolkit.py
+++ b/toolkit.py
@@ -840,7 +840,7 @@ class ClassificationProject(object):
         if self._train_val_idx is None:
             if self.kfold_splits is not None:
                 kfold = KFold(self.kfold_splits, shuffle=True, random_state=self.shuffle_seed)
-                for i, train_val_idx in kfold.split(self.x_train):
+                for i, train_val_idx in enumerate(kfold.split(self.x_train)):
                     if i == self.kfold_index:
                         self._train_val_idx = train_val_idx
                         break