diff --git a/changelog.d/8326.misc b/changelog.d/8326.misc
new file mode 100644
index 000000000000..985d2c027aa9
--- /dev/null
+++ b/changelog.d/8326.misc
@@ -0,0 +1 @@
+Update outdated usages of `metaclass` to python 3 syntax.
\ No newline at end of file
diff --git a/synapse/handlers/room_member.py b/synapse/handlers/room_member.py
index 01a6e882629f..8feba8c90a39 100644
--- a/synapse/handlers/room_member.py
+++ b/synapse/handlers/room_member.py
@@ -51,14 +51,12 @@
 logger = logging.getLogger(__name__)
 
 
-class RoomMemberHandler:
+class RoomMemberHandler(metaclass=abc.ABCMeta):
     # TODO(paul): This handler currently contains a messy conflation of
     #   low-level API that works on UserID objects and so on, and REST-level
     #   API that takes ID strings and returns pagination chunks. These concerns
     #   ought to be separated out a lot better.
 
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, hs: "HomeServer"):
         self.hs = hs
         self.store = hs.get_datastore()
diff --git a/synapse/replication/http/_base.py b/synapse/replication/http/_base.py
index ba16f22c91c1..b448da671038 100644
--- a/synapse/replication/http/_base.py
+++ b/synapse/replication/http/_base.py
@@ -33,7 +33,7 @@
 logger = logging.getLogger(__name__)
 
 
-class ReplicationEndpoint:
+class ReplicationEndpoint(metaclass=abc.ABCMeta):
     """Helper base class for defining new replication HTTP endpoints.
 
     This creates an endpoint under `/_synapse/replication/:NAME/:PATH_ARGS..`
@@ -72,8 +72,6 @@ class ReplicationEndpoint:
             is received.
     """
 
-    __metaclass__ = abc.ABCMeta
-
     NAME = abc.abstractproperty()  # type: str  # type: ignore
     PATH_ARGS = abc.abstractproperty()  # type: Tuple[str, ...]  # type: ignore
     METHOD = "POST"
diff --git a/synapse/storage/databases/main/account_data.py b/synapse/storage/databases/main/account_data.py
index 4436b1a83d97..5f1a2b9aa6cc 100644
--- a/synapse/storage/databases/main/account_data.py
+++ b/synapse/storage/databases/main/account_data.py
@@ -29,15 +29,13 @@
 logger = logging.getLogger(__name__)
 
 
-class AccountDataWorkerStore(SQLBaseStore):
+# The ABCMeta metaclass ensures that it cannot be instantiated without
+# the abstract methods being implemented.
+class AccountDataWorkerStore(SQLBaseStore, metaclass=abc.ABCMeta):
     """This is an abstract base class where subclasses must implement
     `get_max_account_data_stream_id` which can be called in the initializer.
     """
 
-    # This ABCMeta metaclass ensures that we cannot be instantiated without
-    # the abstract methods being implemented.
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, database: DatabasePool, db_conn, hs):
         account_max = self.get_max_account_data_stream_id()
         self._account_data_stream_cache = StreamChangeCache(
diff --git a/synapse/storage/databases/main/push_rule.py b/synapse/storage/databases/main/push_rule.py
index 9790a3199847..b7a8d34ce129 100644
--- a/synapse/storage/databases/main/push_rule.py
+++ b/synapse/storage/databases/main/push_rule.py
@@ -61,6 +61,8 @@ def _load_rules(rawrules, enabled_map, use_new_defaults=False):
     return rules
 
 
+# The ABCMeta metaclass ensures that it cannot be instantiated without
+# the abstract methods being implemented.
 class PushRulesWorkerStore(
     ApplicationServiceWorkerStore,
     ReceiptsWorkerStore,
@@ -68,15 +70,12 @@ class PushRulesWorkerStore(
     RoomMemberWorkerStore,
     EventsWorkerStore,
     SQLBaseStore,
+    metaclass=abc.ABCMeta,
 ):
     """This is an abstract base class where subclasses must implement
     `get_max_push_rules_stream_id` which can be called in the initializer.
     """
 
-    # This ABCMeta metaclass ensures that we cannot be instantiated without
-    # the abstract methods being implemented.
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, database: DatabasePool, db_conn, hs):
         super(PushRulesWorkerStore, self).__init__(database, db_conn, hs)
 
diff --git a/synapse/storage/databases/main/receipts.py b/synapse/storage/databases/main/receipts.py
index 4a0d5a320efb..6568bddd81e6 100644
--- a/synapse/storage/databases/main/receipts.py
+++ b/synapse/storage/databases/main/receipts.py
@@ -31,15 +31,13 @@
 logger = logging.getLogger(__name__)
 
 
-class ReceiptsWorkerStore(SQLBaseStore):
+# The ABCMeta metaclass ensures that it cannot be instantiated without
+# the abstract methods being implemented.
+class ReceiptsWorkerStore(SQLBaseStore, metaclass=abc.ABCMeta):
     """This is an abstract base class where subclasses must implement
     `get_max_receipt_stream_id` which can be called in the initializer.
     """
 
-    # This ABCMeta metaclass ensures that we cannot be instantiated without
-    # the abstract methods being implemented.
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, database: DatabasePool, db_conn, hs):
         super(ReceiptsWorkerStore, self).__init__(database, db_conn, hs)
 
diff --git a/synapse/storage/databases/main/stream.py b/synapse/storage/databases/main/stream.py
index 2e955187524e..7dbe11513b3c 100644
--- a/synapse/storage/databases/main/stream.py
+++ b/synapse/storage/databases/main/stream.py
@@ -259,14 +259,12 @@ def filter_to_clause(event_filter: Optional[Filter]) -> Tuple[str, List[str]]:
     return " AND ".join(clauses), args
 
 
-class StreamWorkerStore(EventsWorkerStore, SQLBaseStore):
+class StreamWorkerStore(EventsWorkerStore, SQLBaseStore, metaclass=abc.ABCMeta):
     """This is an abstract base class where subclasses must implement
     `get_room_max_stream_ordering` and `get_room_min_stream_ordering`
     which can be called in the initializer.
     """
 
-    __metaclass__ = abc.ABCMeta
-
     def __init__(self, database: DatabasePool, db_conn, hs: "HomeServer"):
         super(StreamWorkerStore, self).__init__(database, db_conn, hs)
 
diff --git a/synapse/types.py b/synapse/types.py
index dc09448bdc8d..a6fc7df22c30 100644
--- a/synapse/types.py
+++ b/synapse/types.py
@@ -165,7 +165,9 @@ def get_localpart_from_id(string):
 DS = TypeVar("DS", bound="DomainSpecificString")
 
 
-class DomainSpecificString(namedtuple("DomainSpecificString", ("localpart", "domain"))):
+class DomainSpecificString(
+    namedtuple("DomainSpecificString", ("localpart", "domain")), metaclass=abc.ABCMeta
+):
     """Common base class among ID/name strings that have a local part and a
     domain name, prefixed with a sigil.
 
@@ -175,8 +177,6 @@ class DomainSpecificString(namedtuple("DomainSpecificString", ("localpart", "dom
         'domain' : The domain part of the name
     """
 
-    __metaclass__ = abc.ABCMeta
-
     SIGIL = abc.abstractproperty()  # type: str  # type: ignore
 
     # Deny iteration because it will bite you if you try to create a singleton