diff --git a/synapse/storage/engines/postgres.py b/synapse/storage/engines/postgres.py
index 069aa3485b9..01cd9154f4c 100644
--- a/synapse/storage/engines/postgres.py
+++ b/synapse/storage/engines/postgres.py
@@ -187,7 +187,12 @@ def on_new_connection(self, db_conn: "LoggingDatabaseConnection") -> None:
 
         # Abort really long-running statements and turn them into errors.
         if self.statement_timeout is not None:
-            self.set_statement_timeout(cursor.txn, self.statement_timeout)
+            # Because the PostgresEngine is considered an ABCMeta, a superclass and a
+            # subclass, cursor's type is messy. We know it should be a CursorType,
+            # but for now that doesn't pass cleanly through LoggingDatabaseConnection
+            # and LoggingTransaction. Fortunately, it's merely running an execute()
+            # and nothing more exotic.
+            self.set_statement_timeout(cursor.txn, self.statement_timeout)  # type: ignore[arg-type]
 
         cursor.close()
         db_conn.commit()