diff --git a/config/config.default.yaml b/config/config.default.yaml
index 9f595401..794b2bae 100644
--- a/config/config.default.yaml
+++ b/config/config.default.yaml
@@ -418,10 +418,10 @@ sector:
       heat_loss: 0.0
   heat_pump_sources:
     central:
-      - air
+    - air
     decentral:
-      - air
-      - ground
+    - air
+    - ground
   cluster_heat_buses: true
   heat_demand_cutout: default
   bev_dsm_restriction_value: 0.75