diff --git a/src/sensospot_tools/hdr.py b/src/sensospot_tools/hdr.py
index 32e1a3e..52e770d 100644
--- a/src/sensospot_tools/hdr.py
+++ b/src/sensospot_tools/hdr.py
@@ -1,4 +1,4 @@
-from typing import Union
+from __future__ import annotations
 
 import pandas
 
@@ -8,7 +8,7 @@ from .selection import select
 
 def select_hdr_data(
     data: pandas.DataFrame,
-    spot_id_columns: Union[list[str], str],
+    spot_id_columns: str | list[str],
     time_column: str,
     overflow_column: str,
 ) -> pandas.DataFrame:
@@ -69,9 +69,9 @@ def select_hdr_data(
 
 def normalize(
     data: pandas.DataFrame,
-    normalized_time: Union[int, float],
+    normalized_time: float,
     time_column: str,
-    value_columns: Union[list[str], str],
+    value_columns: str | list[str],
     template: str = "Normalized.{}",
 ) -> pandas.DataFrame:
     """Normalizes values to a normalized exposure time.
diff --git a/src/sensospot_tools/helpers.py b/src/sensospot_tools/helpers.py
index 609bad2..9ff9011 100644
--- a/src/sensospot_tools/helpers.py
+++ b/src/sensospot_tools/helpers.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import itertools
 from typing import Any
 
diff --git a/src/sensospot_tools/selection.py b/src/sensospot_tools/selection.py
index 2fe8865..dec90ed 100644
--- a/src/sensospot_tools/selection.py
+++ b/src/sensospot_tools/selection.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 from typing import Any, Iterator
 
 import pandas