diff --git a/neuralprophet/data/split.py b/neuralprophet/data/split.py
index 875ba885d..6824cdfc2 100644
--- a/neuralprophet/data/split.py
+++ b/neuralprophet/data/split.py
@@ -65,7 +65,7 @@ def _maybe_extend_df(
             future_df["ID"] = df_name
             df_i = pd.concat([df_i, future_df])
             df_i.reset_index(drop=True, inplace=True)
-        extended_df = pd.concat((extended_df, df_i.copy(deep=True)), ignore_index=True)
+        extended_df = pd.concat((extended_df, df_i), ignore_index=True)
     return extended_df, periods_add