diff --git a/Service/Plugins/AccountingService.cs b/Service/Plugins/AccountingService.cs
index 1c9f2a534..62366ced2 100644
--- a/Service/Plugins/AccountingService.cs
+++ b/Service/Plugins/AccountingService.cs
@@ -599,10 +599,10 @@ namespace BeWo.Service.Plugins
 						{
 							if (NewSip.Customer != null && diffRechnung.ServiceInvoicePeriods.Any(s => s.Customer.CustomerOid == NewSip.Customer.CustomerOid) &&
 							NewSip.SupportConceptApprovalPeriod != null && NewSip.SupportConceptApprovalPeriod.SupportConceptApprovalPeriodOid.HasValue
-							&& diffRechnung.ServiceInvoicePeriods.Any(s => s.SupportConceptApprovalPeriod.SupportConceptApprovalPeriodOid.HasValue
+							&& diffRechnung.ServiceInvoicePeriods.Any(s => s.SupportConceptApprovalPeriod != null && s.SupportConceptApprovalPeriod.SupportConceptApprovalPeriodOid.HasValue
 							&& s.SupportConceptApprovalPeriod.SupportConceptApprovalPeriodOid.Value == NewSip.SupportConceptApprovalPeriod.SupportConceptApprovalPeriodOid.Value))
 							{
-								var ip = diffRechnung.ServiceInvoicePeriods.Where(s => s.SupportConceptApprovalPeriod.SupportConceptApprovalPeriodOid.Value == NewSip.SupportConceptApprovalPeriod.SupportConceptApprovalPeriodOid.Value).First();
+								var ip = diffRechnung.ServiceInvoicePeriods.Where(s => s.SupportConceptApprovalPeriod != null && s.SupportConceptApprovalPeriod.SupportConceptApprovalPeriodOid.Value == NewSip.SupportConceptApprovalPeriod.SupportConceptApprovalPeriodOid.Value).First();
                                 if (ip.InvoiceItems != null && ip.InvoiceItems.Count > 0)
                                 {
                                     ip.Claim += NewSip.Claim;