diff --git a/scripts/prepare_sector_network.py b/scripts/prepare_sector_network.py
index 17eb832d..79bc67e9 100644
--- a/scripts/prepare_sector_network.py
+++ b/scripts/prepare_sector_network.py
@@ -286,6 +286,8 @@ def build_carbon_budget(o, input_eurostat, fn, emissions_scope, report_year):
     )
 
     planning_horizons = snakemake.params.planning_horizons
+    if not isinstance(planning_horizons, list):
+        planning_horizons = [planning_horizons]
     t_0 = planning_horizons[0]
 
     if "be" in o: