diff --git a/bob/learn/tensorflow/dataset/bio.py b/bob/learn/tensorflow/dataset/bio.py
index f4ed404c59169333c6fea4f0740e442419c8574a..4a9b66bcc91f8656367739b59bfaf580a355c381 100644
--- a/bob/learn/tensorflow/dataset/bio.py
+++ b/bob/learn/tensorflow/dataset/bio.py
@@ -56,15 +56,20 @@ class BioGenerator(Generator):
         self.load_data = load_data
         self.biofile_to_label = biofile_to_label
 
-        def reader(f):
+        def _reader(f):
             label = int(self.biofile_to_label(f))
             data = self.load_data(self.database, f)
             key = str(f.make_path("", "")).encode("utf-8")
-            if self.multiple_samples:
+            return data, label, key
+
+        if multiple_samples:
+            def reader(f):
+                data, label, key = _reader(f)
                 for d in data:
                     yield (d, label, key)
-            else:
-                yield (data, label, key)
+        else:
+            def reader(f):
+                return _reader(f)
 
         super(BioGenerator, self).__init__(
             biofiles, reader, multiple_samples=multiple_samples, **kwargs