diff --git a/singer_sdk/connectors/sql.py b/singer_sdk/connectors/sql.py
index fa08b73f6..5d86f056a 100644
--- a/singer_sdk/connectors/sql.py
+++ b/singer_sdk/connectors/sql.py
@@ -59,7 +59,7 @@ def __init__(
         self._config: dict[str, t.Any] = config or {}
         self._sqlalchemy_url: str | None = sqlalchemy_url or None
         self._table_cols_cache: dict[str, dict[str, sqlalchemy.Column]] = {}
-        self._schema_cache: set = {}
+        self._schema_cache: t.Set[str] = set()
 
     @property
     def config(self) -> dict: