diff --git a/swh/core/collections.py b/swh/core/collections.py
--- a/swh/core/collections.py
+++ b/swh/core/collections.py
@@ -4,7 +4,6 @@
 # See top-level LICENSE file for more information
 
 import bisect
-import collections
 import itertools
 from typing import Any, Callable, Generic, Iterator, List, Optional, Tuple, TypeVar
 
@@ -12,7 +11,7 @@
 SortedListKey = TypeVar("SortedListKey")
 
 
-class SortedList(collections.UserList, Generic[SortedListKey, SortedListItem]):
+class SortedList(Generic[SortedListKey, SortedListItem]):
     data: List[Tuple[SortedListKey, SortedListItem]]
 
     # https://github.com/python/mypy/issues/708
@@ -29,7 +28,7 @@
                 return item
 
         assert key is not None  # for mypy
-        super().__init__(sorted((key(x), x) for x in data or []))
+        self.data = sorted((key(x), x) for x in data or [])
 
         self.key: Callable[[SortedListItem], SortedListKey] = key
 
diff --git a/swh/core/tests/test_collections.py b/swh/core/tests/test_collections.py
--- a/swh/core/tests/test_collections.py
+++ b/swh/core/tests/test_collections.py
@@ -69,3 +69,18 @@
     for split in items:
         expected = reversed(sorted(item for item in items if item < split))
         assert list(list_.iter_after(-split)) == list(expected), f"split: {split}"
+
+
+@parametrize
+def test_contains(items):
+    list_ = SortedList()
+    for i in range(len(items)):
+        for item in items[0:i]:
+            assert item in list_
+        for item in items[i:]:
+            assert item not in list_
+
+        list_.add(items[i])
+
+    for item in items:
+        assert item in list_