diff --git a/xcdat/temporal.py b/xcdat/temporal.py
index dbdd1203..afd3c994 100644
--- a/xcdat/temporal.py
+++ b/xcdat/temporal.py
@@ -1250,7 +1250,7 @@ def _get_weights(self, time_bounds: xr.DataArray) -> xr.DataArray:
         if isinstance(time_lengths.data, Array):
             time_lengths = time_lengths.astype("timedelta64[ns]")
 
-        time_lengths = time_lengths.astype("float64")
+        time_lengths = time_lengths.astype(np.float64)
 
         grouped_time_lengths = self._group_data(time_lengths)
         weights: xr.DataArray = grouped_time_lengths / grouped_time_lengths.sum()