diff --git a/django/contrib/messages/storage/cookie.py b/django/contrib/messages/storage/cookie.py
index b51e292aa0..1198689968 100644
--- a/django/contrib/messages/storage/cookie.py
+++ b/django/contrib/messages/storage/cookie.py
@@ -14,6 +14,10 @@ class MessageEncoder(json.JSONEncoder):
     """
     message_key = '__json_message'
 
+    def __init__(self, *args, **kwargs):
+        kwargs.setdefault('separators', (',', ':'))
+        super().__init__(*args, **kwargs)
+
     def default(self, obj):
         if isinstance(obj, Message):
             # Using 0/1 here instead of False/True to produce more compact json
@@ -148,7 +152,7 @@ class CookieStorage(BaseStorage):
         also contains a hash to ensure that the data was not tampered with.
         """
         if messages or encode_empty:
-            encoder = MessageEncoder(separators=(',', ':'))
+            encoder = MessageEncoder()
             value = encoder.encode(messages)
             return self.signer.sign(value)
 
diff --git a/django/contrib/messages/storage/session.py b/django/contrib/messages/storage/session.py
index 170c4940ab..b5291f151c 100644
--- a/django/contrib/messages/storage/session.py
+++ b/django/contrib/messages/storage/session.py
@@ -38,7 +38,7 @@ class SessionStorage(BaseStorage):
         return []
 
     def serialize_messages(self, messages):
-        encoder = MessageEncoder(separators=(',', ':'))
+        encoder = MessageEncoder()
         return encoder.encode(messages)
 
     def deserialize_messages(self, data):
diff --git a/tests/messages_tests/test_cookie.py b/tests/messages_tests/test_cookie.py
index 5d5fb42d67..7f4672de8b 100644
--- a/tests/messages_tests/test_cookie.py
+++ b/tests/messages_tests/test_cookie.py
@@ -141,7 +141,7 @@ class CookieTests(BaseTests, SimpleTestCase):
             },
             Message(constants.INFO, 'message %s'),
         ]
-        encoder = MessageEncoder(separators=(',', ':'))
+        encoder = MessageEncoder()
         value = encoder.encode(messages)
         decoded_messages = json.loads(value, cls=MessageDecoder)
         self.assertEqual(messages, decoded_messages)
@@ -166,7 +166,7 @@ class CookieTests(BaseTests, SimpleTestCase):
         storage = self.storage_class(self.get_request())
         messages = ['this', 'that']
         # Encode/decode a message using the pre-Django 3.1 hash.
-        encoder = MessageEncoder(separators=(',', ':'))
+        encoder = MessageEncoder()
         value = encoder.encode(messages)
         encoded_messages = '%s$%s' % (storage._legacy_hash(value), value)
         decoded_messages = storage._decode(encoded_messages)