diff --git a/django/db/backends/base/features.py b/django/db/backends/base/features.py
index 885033361a..42eb59c969 100644
--- a/django/db/backends/base/features.py
+++ b/django/db/backends/base/features.py
@@ -325,7 +325,7 @@ class BaseDatabaseFeatures:
 
     # A set of dotted paths to tests in Django's test suite that are expected
     # to fail on this database.
-    django_test_expected_failures = {}
+    django_test_expected_failures = set()
     # A map of reasons to sets of dotted paths to tests in Django's test suite
     # that should be skipped for this database.
     django_test_skips = {}