diff -r 1ce77362598f -r a902f158b4fc src/Pure/ProofGeneral/pgip_parser.ML
--- a/src/Pure/ProofGeneral/pgip_parser.ML	Tue Jul 20 14:41:13 2010 +0200
+++ b/src/Pure/ProofGeneral/pgip_parser.ML	Tue Jul 20 14:44:33 2010 +0200
@@ -78,7 +78,7 @@
   |> command Keyword.prf_script       proofstep;
 
 val _ = subset (op =) (Keyword.kinds, Symtab.keys command_keywords)
-  orelse sys_error "Incomplete coverage of command keywords";
+  orelse raise Fail "Incomplete coverage of command keywords";
 
 fun parse_command "sorry" text = [D.Postponegoal {text = text}, D.Closeblock {}]
   | parse_command name text =