diff --git a/src/toargridding/grids.py b/src/toargridding/grids.py
index 46b6c68f4515ffab5df830d5753eab2b67dd90a6..0d3ade83a0fe068ae0277ecb3d50a016093fe330 100644
--- a/src/toargridding/grids.py
+++ b/src/toargridding/grids.py
@@ -166,7 +166,7 @@ class RegularGrid(GridDefinition):
         cell_indices = self.as_cell_index(coords)
 
         # will convert cell_indices to float as some nans ar present
-        data_with_indices = data.join(cell_indices.to_frame(GridDefinition.cell_index_name), how="outer")
+        data_with_indices = data.join(cell_indices.to_frame(GridDefinition.cell_index_name), how="inner")
 
         return data_with_indices.groupby(GridDefinition.cell_index_name)