diff --git a/bob/learn/tensorflow/data/generator.py b/bob/learn/tensorflow/data/generator.py
index bcf0e79aad70d5ffe004e97af88621c29851eb10..f772051839e5769144b66e941bf3e3f35eb4788c 100644
--- a/bob/learn/tensorflow/data/generator.py
+++ b/bob/learn/tensorflow/data/generator.py
@@ -76,10 +76,12 @@ class Generator:
 
     @property
     def output_types(self):
+        "The types of the returned samples."
         return self._output_types
 
     @property
     def output_shapes(self):
+        "The shapes of the returned samples."
         return self._output_shapes
 
     def __call__(self):