diff --git a/mlair/data_handler/default_data_handler.py b/mlair/data_handler/default_data_handler.py
index a17de95407a74d1504877fdce03a82d1c943e868..35959582a9aa18ee412ed99a69bc75612641e42a 100644
--- a/mlair/data_handler/default_data_handler.py
+++ b/mlair/data_handler/default_data_handler.py
@@ -230,14 +230,16 @@ class DefaultDataHandler(AbstractDataHandler):
             else:
                 extreme_idx = xr.concat([(Y < -extr_val).any(dim=other_dims[0]),
                                            (Y > extr_val).any(dim=other_dims[0])],
-                                          dim=other_dims[1]).any(dim=other_dims[1])
+                                          dim=other_dims[0]).any(dim=other_dims[0])
 
-            extremes_X = list(map(lambda x: x.sel(**{dim: extreme_idx}), X))
+            sel = extreme_idx[extreme_idx].coords[dim].values
+            extremes_X = list(map(lambda x: x.sel(**{dim: sel}), X))
             self._add_timedelta(extremes_X, dim, timedelta)
             # extremes_X = list(map(lambda x: x.coords[dim].values + np.timedelta64(*timedelta), extremes_X))
 
             extremes_Y = Y.sel(**{dim: extreme_idx})
-            extremes_Y.coords[dim].values += np.timedelta64(*timedelta)
+            #extremes_Y.coords[dim].values += np.timedelta64(*timedelta)
+            self._add_timedelta(extremes_Y, dim, timedelta)
 
             self._Y_extreme = xr.concat([Y, extremes_Y], dim=dim)
             self._X_extreme = list(map(lambda x1, x2: xr.concat([x1, x2], dim=dim), X, extremes_X))
@@ -245,7 +247,7 @@ class DefaultDataHandler(AbstractDataHandler):
     @staticmethod
     def _add_timedelta(data, dim, timedelta):
         for d in data:
-            d.coords[dim].values += np.timedelta64(*timedelta)
+            d.coords[dim] = d.coords[dim].values + np.timedelta64(*timedelta)
 
     @classmethod
     def transformation(cls, set_stations, **kwargs):