diff --git a/mlair/data_handler/data_handler_wrf_chem.py b/mlair/data_handler/data_handler_wrf_chem.py
index 2d0ea525be9340b2065397eb5e78d41ae202655a..1d42649bdde2b571ff9ba77dd8d3027386ae275d 100644
--- a/mlair/data_handler/data_handler_wrf_chem.py
+++ b/mlair/data_handler/data_handler_wrf_chem.py
@@ -1254,7 +1254,7 @@ class DataHandlerSectorGrid(DataHandlerSingleGridColumn):
         wind_upstream_sector_by_name = self.wind_upstream_sector_by_name
         dims_to_expand = list(wind_upstream_sector_by_name.coords._names - set(wind_upstream_sector_by_name.dims))
         wind_upstream_sector_by_name = wind_upstream_sector_by_name.expand_dims(dims_to_expand).squeeze(
-            dim=list(set(dims_to_expand) - {self.iter_dim, self.target_dim}))
+            dim=list(set(dims_to_expand) - {self.iter_dim, self.target_dim}), drop=True)
         wind_upstream_sector_by_name = wind_upstream_sector_by_name.to_dataset(self.iter_dim)
         wind_upstream_sector_by_name.to_netcdf(file_name)