diff --git a/telethon/_sessions/sqlite.py b/telethon/_sessions/sqlite.py
index 7b0e5849..791f4818 100644
--- a/telethon/_sessions/sqlite.py
+++ b/telethon/_sessions/sqlite.py
@@ -39,7 +39,7 @@ class SQLiteSession(Session):
         self.save_entities = True
 
         if session_id:
-            self.filename = session_id
+            self.filename = os.fspath(session_id)
             if not self.filename.endswith(EXTENSION):
                 self.filename += EXTENSION