diff --git a/lib/open_food_network/user_balance_calculator.rb b/lib/open_food_network/user_balance_calculator.rb
index 5ce083e10f..98af1600f9 100644
--- a/lib/open_food_network/user_balance_calculator.rb
+++ b/lib/open_food_network/user_balance_calculator.rb
@@ -6,7 +6,7 @@ module OpenFoodNetwork
     end
 
     def balance
-      -completed_orders.sum(&:outstanding_balance)
+      -completed_orders.to_a.sum(&:outstanding_balance)
     end
 
     private