diff -r be79948f7f23 -r 4d27b520622a src/Pure/Thy/export_theory.scala
--- a/src/Pure/Thy/export_theory.scala	Fri Aug 05 18:45:49 2022 +0200
+++ b/src/Pure/Thy/export_theory.scala	Fri Aug 05 19:02:38 2022 +0200
@@ -108,7 +108,7 @@
   }
 
   def read_theory_parents(provider: Export.Provider, theory_name: String): Option[List[String]] =
-    provider.focus(theory_name)(Export.THEORY_PREFIX + "parents")
+    provider.focus(theory_name)(Export.THEORY_PARENTS)
       .map(entry => Library.trim_split_lines(entry.uncompressed.text))
 
   def no_theory: Theory =