diff --git a/ReportImp/LebenshilfeCoburg/CollectiveBillingReport.cs b/ReportImp/LebenshilfeCoburg/CollectiveBillingReport.cs
index a1154b928..1ca064fa8 100644
--- a/ReportImp/LebenshilfeCoburg/CollectiveBillingReport.cs
+++ b/ReportImp/LebenshilfeCoburg/CollectiveBillingReport.cs
@@ -24,7 +24,7 @@ namespace LebenshilfeCoburg
 	        }
 	        if (pRO.ServiceInvoicePeriods != null)
 	        {
-                pRO.ServiceInvoicePeriods.OrderBy(sip => sip.Customer.LastName);
+                pRO.ServiceInvoicePeriods = pRO.ServiceInvoicePeriods.OrderBy(sip => sip.Customer.LastName).ToList();
 
 		        foreach (var sip in pRO.ServiceInvoicePeriods)
 		        {