diff --git a/Lib/test/test_shelve.py b/Lib/test/test_shelve.py
index 64609ab9dd9a62..5f6a030e018f96 100644
--- a/Lib/test/test_shelve.py
+++ b/Lib/test/test_shelve.py
@@ -5,7 +5,7 @@
 import pickle
 import os
 
-from test.support import import_helper, os_helper
+from test.support import import_helper, os_helper, subTests
 from collections.abc import MutableMapping
 from test.test_dbm import dbm_iterator
 
@@ -173,6 +173,8 @@ def test_custom_serializer_and_deserializer(self):
         def serializer(obj, protocol):
             if isinstance(obj, (bytes, bytearray, str)):
                 if protocol == 5:
+                    if isinstance(obj, bytearray):
+                        return bytes(obj)  # DBM backends expect bytes
                     return obj
                 return type(obj).__name__
             elif isinstance(obj, array.array):
@@ -222,22 +224,31 @@ def deserializer(data):
                         s["array_data"], array_data.tobytes().decode()
                     )
 
-    def test_custom_incomplete_serializer_and_deserializer(self):
-        dbm_sqlite3 = import_helper.import_module("dbm.sqlite3")
-        os.mkdir(self.dirname)
-        self.addCleanup(os_helper.rmtree, self.dirname)
+    @subTests("serialized", [None, ["invalid type"]])
+    def test_custom_invalid_serializer(self, serialized):
+        test_dir = f"{self.dirname}_{id(serialized)}"
+        os.mkdir(test_dir)
+        self.addCleanup(os_helper.rmtree, test_dir)
+        test_fn = os.path.join(test_dir, "shelftemp.db")
 
-        with self.assertRaises(dbm_sqlite3.error):
-            def serializer(obj, protocol=None):
-                pass
+        def serializer(obj, protocol=None):
+            return serialized
 
-            def deserializer(data):
-                return data.decode("utf-8")
+        def deserializer(data):
+            return data.decode("utf-8")
 
-            with shelve.open(self.fn, serializer=serializer,
+        # Since the serializer returns an invalid type or None,
+        # dbm.error is raised by dbm.sqlite3 and TypeError is raised
+        # by other backends.
+        with self.assertRaises((TypeError, dbm.error)):
+            with shelve.open(test_fn, serializer=serializer,
                              deserializer=deserializer) as s:
                 s["foo"] = "bar"
 
+    def test_custom_incomplete_deserializer(self):
+        os.mkdir(self.dirname)
+        self.addCleanup(os_helper.rmtree, self.dirname)
+
         def serializer(obj, protocol=None):
             return type(obj).__name__.encode("utf-8")
 
@@ -352,7 +363,7 @@ def type_name_len(obj):
                     self.assertEqual(s["bytearray_data"], "bytearray")
                     self.assertEqual(s["array_data"], "array")
 
-    def test_custom_incomplete_serializer_and_deserializer_bsd_db_shelf(self):
+    def test_custom_incomplete_deserializer_bsd_db_shelf(self):
         berkeleydb = import_helper.import_module("berkeleydb")
         os.mkdir(self.dirname)
         self.addCleanup(os_helper.rmtree, self.dirname)
@@ -370,6 +381,11 @@ def deserializer(data):
             self.assertIsNone(s["foo"])
             self.assertNotEqual(s["foo"], "bar")
 
+    def test_custom_incomplete_serializer_bsd_db_shelf(self):
+        berkeleydb = import_helper.import_module("berkeleydb")
+        os.mkdir(self.dirname)
+        self.addCleanup(os_helper.rmtree, self.dirname)
+
         def serializer(obj, protocol=None):
             pass