diff --git a/aerich/ddl/__init__.py b/aerich/ddl/__init__.py
index 50d2ea5..de76ae8 100644
--- a/aerich/ddl/__init__.py
+++ b/aerich/ddl/__init__.py
@@ -5,7 +5,6 @@ from typing import Any, List, Type, cast
 import tortoise
 from tortoise import BaseDBAsyncClient, Model
 from tortoise.backends.base.schema_generator import BaseSchemaGenerator
-from tortoise.backends.sqlite.schema_generator import SqliteSchemaGenerator
 
 from aerich.utils import is_default_function
 
@@ -128,11 +127,7 @@ class BaseDDL:
             template = self._MODIFY_COLUMN_TEMPLATE
         else:
             # sqlite does not support alter table to add unique column
-            unique = (
-                " UNIQUE"
-                if field_describe.get("unique") and self.DIALECT != SqliteSchemaGenerator.DIALECT
-                else ""
-            )
+            unique = " UNIQUE" if field_describe.get("unique") and self.DIALECT != "sqlite" else ""
             template = self._ADD_COLUMN_TEMPLATE
         column = self.schema_generator._create_string(
             db_column=db_column,