diff --git a/django/test/runner.py b/django/test/runner.py
index 0d01b9b61d..2619fe4504 100644
--- a/django/test/runner.py
+++ b/django/test/runner.py
@@ -233,7 +233,11 @@ def _init_worker(counter):
     for alias in connections:
         connection = connections[alias]
         settings_dict = connection.creation.get_test_db_clone_settings(_worker_id)
-        connection.settings_dict = settings_dict
+        # connection.settings_dict must be updated in place for changes to be
+        # reflected in django.db.connections. If the following line assigned
+        # connection.settings_dict = settings_dict, new threads would connect
+        # to the default database instead of the appropriate clone.
+        connection.settings_dict.update(settings_dict)
         connection.close()