diff --git a/swh/core/tests/test_utils.py b/swh/core/tests/test_utils.py
--- a/swh/core/tests/test_utils.py
+++ b/swh/core/tests/test_utils.py
@@ -1,4 +1,4 @@
-# Copyright (C) 2015-2017  The Software Heritage developers
+# Copyright (C) 2015-2018  The Software Heritage developers
 # See the AUTHORS file at the top-level directory of this distribution
 # License: GNU General Public License version 3, or any later version
 # See top-level LICENSE file for more information
@@ -29,6 +29,30 @@
 
         self.assertEqual(out, [[9, 8, 7, 6], [5, 4, 3, 2], [1]])
 
+    def test_grouper_with_stop_value(self):
+        # given
+        actual_data = utils.grouper(((i, i+1) for i in range(0, 9)), 2)
+
+        out = []
+        for d in actual_data:
+            out.append(list(d))  # force generator resolution for checks
+
+        self.assertEqual(out, [
+            [(0, 1), (1, 2)],
+            [(2, 3), (3, 4)],
+            [(4, 5), (5, 6)],
+            [(6, 7), (7, 8)],
+            [(8, 9)]])
+
+        # given
+        actual_data = utils.grouper((i for i in range(9, 0, -1)), 4)
+
+        out = []
+        for d in actual_data:
+            out.append(list(d))  # force generator resolution for checks
+
+        self.assertEqual(out, [[9, 8, 7, 6], [5, 4, 3, 2], [1]])
+
     def test_backslashescape_errors(self):
         raw_data_err = b'abcd\x80'
         with self.assertRaises(UnicodeDecodeError):
diff --git a/swh/core/utils.py b/swh/core/utils.py
--- a/swh/core/utils.py
+++ b/swh/core/utils.py
@@ -26,20 +26,27 @@
 
 
 def grouper(iterable, n):
-    """Collect data into fixed-length chunks or blocks.
+    """Collect data into fixed-length size iterables. The last block might
+       contain less elements as it will hold only the remaining number
+       of elements.
+
+       The invariant here is that the number of elements in the input
+       iterable and the sum of the number of elements of all iterables
+       generated from this function should be equal.
 
     Args:
-        iterable: an iterable
-        n: size of block
-        fillvalue: value to use for the last block
+        iterable (Iterable): an iterable
+        n (int): size of block to slice the iterable into
 
-    Returns:
-        fixed-length chunks of blocks as iterables
+    Yields:
+        fixed-length blocks as iterables. As mentioned, the last
+        iterable might be less populated.
 
     """
     args = [iter(iterable)] * n
-    for _data in itertools.zip_longest(*args, fillvalue=None):
-        yield (d for d in _data if d is not None)
+    stop_value = object()
+    for _data in itertools.zip_longest(*args, fillvalue=stop_value):
+        yield (d for d in _data if d is not stop_value)
 
 
 def backslashescape_errors(exception):