diff --git a/OBIA/OBIABase.py b/OBIA/OBIABase.py
index f4ea65c74a4ad192150269311dc05caa420d2489..9783bc33463591f1abb5f209d76691bb51c73d7e 100644
--- a/OBIA/OBIABase.py
+++ b/OBIA/OBIABase.py
@@ -377,14 +377,14 @@ class OBIABase:
             self.populate_map(tn,obj_id,classes,output_file,compress)
 
     def true_pred_bypixel(self, labels, predicted_classes, class_field='class'):
-        pred_c = np.zeros(np.max(self.ref_db['orig_label']).astype(int)+1)
+        pred_c = np.zeros(int(np.max(self.ref_db['orig_label']))+1)
         pred_c[labels] = predicted_classes
         support = []
         for tn, t in self.tiled_objects(on_ref=True):
             support.append(t[np.isin(t, labels)])
         support = np.concatenate(support)
         pred = pred_c[support]
-        true_c = np.zeros(np.max(self.ref_db['orig_label']).astype(int)+1)
+        true_c = np.zeros(int(np.max(self.ref_db['orig_label']))+1)
         # ATTENTION: works if "labels" is sorted (as provided by get_reference_...)
         true_c[labels] = self.ref_db.loc[self.ref_db['orig_label'].isin(labels),class_field].to_numpy(dtype=int)
         true = true_c[support]