diff --git a/freqtrade/freqai/data_kitchen.py b/freqtrade/freqai/data_kitchen.py
index c0becd5ae..8a03f5999 100644
--- a/freqtrade/freqai/data_kitchen.py
+++ b/freqtrade/freqai/data_kitchen.py
@@ -960,7 +960,7 @@ class FreqaiDataKitchen:
             append_df[f"{label}_std"] = self.data["labels_std"][label]
 
         for extra_col in self.data["extra_returns_per_train"]:
-            append_df["{extra_col}"] = self.data["extra_returns_per_train"][extra_col]
+            append_df[f"{extra_col}"] = self.data["extra_returns_per_train"][extra_col]
 
         append_df["do_predict"] = do_predict
         if self.freqai_config["feature_parameters"].get("DI_threshold", 0) > 0: