diff --git a/exasol/analytics/query_handler/query/result/udf_query_result.py b/exasol/analytics/query_handler/query/result/udf_query_result.py
index 0e36212c..b051d322 100644
--- a/exasol/analytics/query_handler/query/result/udf_query_result.py
+++ b/exasol/analytics/query_handler/query/result/udf_query_result.py
@@ -1,12 +1,12 @@
 import collections
-from typing import Any, Iterator, List, OrderedDict, Union
+import pandas
+from typing import Any, Iterator, List, Optional, OrderedDict, Union
 
 from exasol.analytics.query_handler.query.result.interface import QueryResult, Row
 from exasol.analytics.schema.column import Column
 from exasol.analytics.schema.column_name import ColumnName
 from exasol.analytics.schema.column_type import ColumnType
 
-
 class UDFQueryResult(QueryResult):
 
     def __init__(
@@ -51,7 +51,7 @@ def rowcount(self) -> int:
 
     def fetch_as_dataframe(
         self, num_rows: Union[str, int], start_col: int = 0
-    ) -> "pandas.DataFrame":  # type: ignore
+    ) -> Optional[pandas.DataFrame]:
         df = self._ctx.get_dataframe(num_rows, start_col=self._start_col)
         self._initialized = True
         if df is None: