diff --git a/app/models/ticket/number/date.rb b/app/models/ticket/number/date.rb
index a8cddca8c..609488532 100644
--- a/app/models/ticket/number/date.rb
+++ b/app/models/ticket/number/date.rb
@@ -43,6 +43,14 @@ module Ticket::Number::Date
     # vehikel number. The modulus to 10 of this sum is substracted from
     # 10. See: http://www.pruefziffernberechnung.de/F/Fahrzeugnummer.shtml
     # (german)
+
+    # fix for https://github.com/zammad/zammad/issues/413 - can be removed later
+    if config.class == FalseClass || config.class == TrueClass
+      config = {
+        checksum: config
+      }
+    end
+
     if config[:checksum]
       chksum = 0
       mult   = 1