diff --git a/databasez/core/database.py b/databasez/core/database.py
index 1f564e7..70da951 100644
--- a/databasez/core/database.py
+++ b/databasez/core/database.py
@@ -449,6 +449,8 @@ async def drop_all(self, meta: MetaData, **kwargs: typing.Any) -> None:
 
     @multiloop_protector(False)
     def connection(self) -> Connection:
+        if not self.is_connected:
+            raise RuntimeError("Database is not connected")
         if self.force_rollback:
             return typing.cast(Connection, self._global_connection)
 
diff --git a/databasez/sqlalchemy.py b/databasez/sqlalchemy.py
index c2cdcfe..75884ed 100644
--- a/databasez/sqlalchemy.py
+++ b/databasez/sqlalchemy.py
@@ -295,5 +295,6 @@ async def connect(self, database_url: DatabaseURL, **options: typing.Any) -> Non
 
     async def disconnect(self) -> None:
         engine = self.engine
+        self.engine = None
         assert engine is not None, "database is not initialized"
         await engine.dispose()