diff --git a/src/npc/newSlaveIncestSex.tw b/src/npc/newSlaveIncestSex.tw
index ac87a2082afe97c73e6c52ba8fcf722956df0603..9c44977e0b5666014c29236cec1d024633635c6b 100644
--- a/src/npc/newSlaveIncestSex.tw
+++ b/src/npc/newSlaveIncestSex.tw
@@ -49,8 +49,16 @@
 <</if>>
 
 <<if _one == _other >>
-/* two sisters / brothers: identify by age */
-	<<if $relative.actualAge > $relative2.actualAge>>
+/* two sisters / brothers: identify by age, in the case of same age twins check their birthWeek */
+	<<if $relative.actualAge == $relative2.actualAge>>
+		<<if $relative.birthWeek >= $relative2.birthWeek>>
+			<<set _onelong = "older "+_one >>
+			<<set _otherlong = "younger "+_other >>
+		<<elseif $relative.birthWeek < $relative2.birthWeek>>
+			<<set _onelong = "younger "+_one >>
+			<<set _otherlong = "older "+_other >>
+		<</if>>
+	<<elseif $relative.actualAge > $relative2.actualAge>>
 		<<set _onelong = "older "+_one >>
 		<<set _otherlong = "younger "+_other >>
 	<<elseif $relative.actualAge < $relative2.actualAge>>