diff --git a/mbtrack2/utilities/misc.py b/mbtrack2/utilities/misc.py
index ec7d4ff9c6c7def41d54fa9965b882b927f88c64..c31af03d547338323c8ca1d98e886eefd02fe853 100644
--- a/mbtrack2/utilities/misc.py
+++ b/mbtrack2/utilities/misc.py
@@ -304,6 +304,6 @@ def double_sided_impedance(impedance):
         except KeyError:
             pass
 
-        all_data = impedance.data.append(negative_data)
+        all_data = pd.concat([impedance.data, negative_data])
         all_data = all_data.sort_index()
         impedance.data = all_data