diff --git a/mlair/helpers/filter.py b/mlair/helpers/filter.py
index 03065402c10c10cf151e05220e70ffe513b4094c..6c4247f3242d0f79e57636379bcc5d3be6e278ba 100644
--- a/mlair/helpers/filter.py
+++ b/mlair/helpers/filter.py
@@ -586,8 +586,8 @@ class ClimateFIRFilter(FIRFilter):
                                                        new_dim).sel({time_dim: t0})
                 else:
                     tmp_filter_data = None
-                valid_start = int(filtered.window.min()) + int((len(h) + 1) / 2)
-                valid_end = min(extend_length_opts + offset + 1, int(filtered.window.max()) - int((len(h) + 1) / 2))
+                valid_start = int(filtered[new_dim].min()) + int((len(h) + 1) / 2)
+                valid_end = min(extend_length_opts + offset + 1, int(filtered[new_dim].max()) - int((len(h) + 1) / 2))
                 valid_range = range(valid_start, valid_end)
                 plot_data.append({"t0": t0,
                                   "var": variable_name,