diff --git a/omnipath_server/loader/_legacy.py b/omnipath_server/loader/_legacy.py
index 8a0a9f6..83bed03 100644
--- a/omnipath_server/loader/_legacy.py
+++ b/omnipath_server/loader/_legacy.py
@@ -13,6 +13,7 @@
 # https://www.gnu.org/licenses/gpl-3.0.txt
 #
 
+from typing import TYPE_CHECKING
 from collections.abc import Generator
 import re
 import bz2
@@ -24,6 +25,10 @@
 from pypath_common import _misc
 from sqlalchemy.orm import decl_api
 
+if TYPE_CHECKING:
+
+    from sqlalchemy.sql.base import ReadOnlyColumnCollection
+
 from .. import _log, _connection
 from ..schema import _legacy as _schema
 
@@ -136,7 +141,7 @@ def _load_table(self, tbl: str):
                     compr_path,
                     schema,
                     self.con,
-                    wipe = self.wipe
+                    wipe = self.wipe,
                 ).load()
 
         _log(
@@ -200,7 +205,7 @@ def load(self) -> None:
 
 
     @property
-    def columns(self) -> 'ReadOnlyColumnCollection':
+    def columns(self) -> ReadOnlyColumnCollection:
 
         return self.table.__table__.columns
 
@@ -249,7 +254,7 @@ def _read(self) -> Generator[tuple, None, None]:
                         sep = getattr(
                             self.table,
                             '_array_sep',
-                            {}
+                            {},
                         ).get(col, ';')
 
                         row[col] = row[col].split(sep) if row[col] else []