diff --git a/openstef/model/fallback.py b/openstef/model/fallback.py
index 68ab9170..924e091f 100644
--- a/openstef/model/fallback.py
+++ b/openstef/model/fallback.py
@@ -65,7 +65,7 @@ def generate_fallback(
             .merge(
                 highest_daily_loadprofile, left_on="time", right_on="time", how="outer"
             )
-            .set_index(forecast.index)
+            .set_index("index")
         )
 
     # Rename so column is called forecast
diff --git a/setup.py b/setup.py
index cbe4217f..049f9353 100644
--- a/setup.py
+++ b/setup.py
@@ -29,7 +29,7 @@ def read_long_description_from_readme():
 
 setup(
     name="openstef",
-    version="3.4.50",
+    version="3.4.51",
     packages=find_packages(include=["openstef", "openstef.*"]),
     description="Open short term energy forecaster",
     long_description=read_long_description_from_readme(),