diff -r 7164f537370f -r 2b2c09f4e7b5 src/Pure/Thy/export_theory.scala
--- a/src/Pure/Thy/export_theory.scala	Sun Aug 14 11:39:28 2022 +0200
+++ b/src/Pure/Thy/export_theory.scala	Sun Aug 14 12:01:47 2022 +0200
@@ -101,7 +101,7 @@
   }
 
   def read_theory_parents(theory_context: Export.Theory_Context): Option[List[String]] =
-    theory_context.get(Export.THEORY_PARENTS)
+    theory_context.get(Export.THEORY_PREFIX + "parents")
       .map(entry => Library.trim_split_lines(entry.uncompressed.text))
 
   def no_theory: Theory =