diff --git a/bob/bio/base/extractor/Extractor.py b/bob/bio/base/extractor/Extractor.py
index c37e4439f42a98e33f2e17e607d44e93fca49004..5cc5f46dfcf6565f8d2ac71f082a8684dda0fa7d 100644
--- a/bob/bio/base/extractor/Extractor.py
+++ b/bob/bio/base/extractor/Extractor.py
@@ -6,6 +6,8 @@
 import os
 
 from .. import utils
+import warnings
+
 
 class Extractor (object):
   """This is the base class for all feature extractors.
diff --git a/bob/bio/base/preprocessor/Preprocessor.py b/bob/bio/base/preprocessor/Preprocessor.py
index dc5d7e47573c209744254a560fb17196c723439d..197182aab2367c6716efc1178a66ca24fb79d837 100644
--- a/bob/bio/base/preprocessor/Preprocessor.py
+++ b/bob/bio/base/preprocessor/Preprocessor.py
@@ -5,6 +5,7 @@
 
 from .. import utils
 
+import warnings
 
 class Preprocessor (object):
     """This is the base class for all preprocessors.