diff --git a/mlair/helpers/join.py b/mlair/helpers/join.py
index f66b277bbca54bd6190ab0430c9f8c0307b3f5af..4683ba2acd6ae5d4090591234b50c3bfae27bffe 100644
--- a/mlair/helpers/join.py
+++ b/mlair/helpers/join.py
@@ -46,7 +46,7 @@ def download_join(station_name: Union[str, List[str]], stat_var: dict, station_t
 
     # correct stat_var values if data is not aggregated (hourly)
     if sampling == "hourly":
-        [stat_var.update({k: "values"}) for k in stat_var.keys()]
+        stat_var = {key: "values" for key in stat_var.keys()}
 
     # download all variables with given statistic
     data = None