diff --git a/Interfaces/ZUGFeRDInterface.vb b/Interfaces/ZUGFeRDInterface.vb
index 1b24c0f2..5031a5d9 100644
--- a/Interfaces/ZUGFeRDInterface.vb
+++ b/Interfaces/ZUGFeRDInterface.vb
@@ -16,6 +16,7 @@ Public Class ZUGFeRDInterface
         NoZugferd
         NoValidZugferd
         MissingProperties
+        UnknownError
     End Enum
 
     Public ReadOnly Property FileGroup As FileGroups