diff -r 52d5067ca06a -r 06cc31dff138 src/Pure/Isar/parse.scala
--- a/src/Pure/Isar/parse.scala	Tue Mar 18 16:45:14 2014 +0100
+++ b/src/Pure/Isar/parse.scala	Tue Mar 18 17:39:03 2014 +0100
@@ -64,7 +64,7 @@
     def path: Parser[String] =
       atom("file name/path specification", tok => tok.is_name && Path.is_wellformed(tok.content))
     def theory_name: Parser[String] =
-      atom("theory name", tok => tok.is_name && Thy_Load.is_wellformed(tok.content))
+      atom("theory name", tok => tok.is_name && Resources.is_wellformed_thy_path(tok.content))
 
     private def tag_name: Parser[String] =
       atom("tag name", tok =>