diff --git a/conf/flight_plans/flight_plan.dtd b/conf/flight_plans/flight_plan.dtd
index 7d1fbdeb12..fb18d5ce0e 100644
--- a/conf/flight_plans/flight_plan.dtd
+++ b/conf/flight_plans/flight_plan.dtd
@@ -159,7 +159,8 @@ var CDATA #REQUIRED
 value CDATA #REQUIRED>
 
 <!ATTLIST call
-fun CDATA #REQUIRED>
+fun CDATA #REQUIRED
+until CDATA #IMPLIED>
 
 <!ATTLIST follow
 ac_id CDATA #REQUIRED
@@ -211,7 +212,8 @@ until CDATA #IMPLIED>
 grid CDATA #REQUIRED
 orientation CDATA #IMPLIED
 wp1 CDATA #REQUIRED
-wp2 CDATA #REQUIRED>
+wp2 CDATA #REQUIRED
+until CDATA #IMPLIED>
 
 <!ATTLIST stay
 wp CDATA #REQUIRED