diff --git a/private_includes/book/toc_include.ily b/private_includes/book/toc_include.ily
index 1c96cce..2b90d17 100644
--- a/private_includes/book/toc_include.ily
+++ b/private_includes/book/toc_include.ily
@@ -318,8 +318,11 @@ indexSection =
             (compositionIds (find-author-ids-by 'composition authors))
             (adaptionIds (find-author-ids-by 'adaption authors))
             (bridgeIds (find-author-ids-by 'bridge authors))
-            (interludeIds (find-author-ids-by 'interlude authors)))
-        (delete-duplicates
+            (interludeIds (find-author-ids-by 'interlude authors))
+            (realAuthorIds (map car AUTHOR_DATA)))
+        (lset-intersection
+          equal?
+          realAuthorIds
           (append poetIds translatorIds (map car versePoetData) composerIds (map car verseComposerData) refComposerIds (map car voiceComposerData) compositionIds adaptionIds bridgeIds interludeIds))
     ))
     (let*