diff --git a/thys/Lambda_Free_RPOs/ROOT b/thys/Lambda_Free_RPOs/ROOT
--- a/thys/Lambda_Free_RPOs/ROOT
+++ b/thys/Lambda_Free_RPOs/ROOT
@@ -1,10 +1,11 @@
 chapter AFP
 
 session Lambda_Free_RPOs (AFP) = "HOL-Library" +
   options [timeout = 600]
   sessions
     "HOL-Cardinals"
+    "Nested_Multisets_Ordinals"
   theories
     Lambda_Free_RPOs
   document_files
     "root.tex"