diff --git a/src/openqdc/datasets/base.py b/src/openqdc/datasets/base.py
index 1c1a2c6..392144d 100644
--- a/src/openqdc/datasets/base.py
+++ b/src/openqdc/datasets/base.py
@@ -159,10 +159,12 @@ def read_preprocess(self):
         for key in ["name", "subset"]:
             filename = p_join(self.preprocess_path, f"{key}.npz")
             pull_locally(filename)
-            # with open(filename, "rb") as f:
-            self.data[key] = np.load(open(filename, "rb"))
-            for k in self.data[key]:
-                print(f"Loaded {key}_{k} with shape {self.data[key][k].shape}, dtype {self.data[key][k].dtype}")
+            self.data[key] = dict()
+            with open(filename, "rb") as f:
+                tmp = np.load(f)
+                for k in tmp:
+                    self.data[key][k] = tmp[k]
+                    print(f"Loaded {key}_{k} with shape {self.data[key][k].shape}, dtype {self.data[key][k].dtype}")
 
     def is_preprocessed(self):
         predicats = [copy_exists(p_join(self.preprocess_path, f"{key}.mmap")) for key in self.data_keys]