diff -r e8197ea2703b -r 0ef08aa52f2e lib/Tools/emacs
--- a/lib/Tools/emacs	Sun Oct 05 13:13:48 2008 +0200
+++ b/lib/Tools/emacs	Mon Oct 06 22:35:03 2008 +0200
@@ -17,6 +17,8 @@
 
 ## main
 
+[ -z "$PROOFGENERAL_HOME" ] && fail "Missing Proof General installation (PROOFGENERAL_HOME)"
+
 INTERFACE="$PROOFGENERAL_HOME/isar/interface"
 [ ! -x "$INTERFACE" ] && fail "Bad interface script: \"$INTERFACE\""