diff --git a/cereslib/dfutils/format.py b/cereslib/dfutils/format.py
index 4035367..1e8c3d5 100644
--- a/cereslib/dfutils/format.py
+++ b/cereslib/dfutils/format.py
@@ -71,7 +71,7 @@ def update_field_names(self, data, matching):
 
         for key in matching.keys():
             if key in data.columns:
-                data.rename(columns={key: matching[key]})
+                data = data.rename(columns={key: matching[key]})
 
         return data