diff -r 4c53227f4b73 -r 8c7706b053c7 src/Pure/Thy/sessions.ML
--- a/src/Pure/Thy/sessions.ML	Wed Sep 11 20:48:10 2019 +0200
+++ b/src/Pure/Thy/sessions.ML	Thu Sep 12 13:33:09 2019 +0200
@@ -86,7 +86,7 @@
               val {node_name, theory_name, ...} =
                 Resources.import_name session session_dir s
                   handle ERROR msg => error (msg ^ Position.here pos);
-              val theory_path = the_default node_name (Resources.known_theory theory_name);
+              val theory_path = the_default node_name (Resources.find_theory_file theory_name);
               val _ = Resources.check_file ctxt (SOME Path.current) (Path.implode theory_path, pos);
             in () end);