--- routines/signal/sigelm.f.orig	Mon Feb  5 10:19:36 2001
+++ routines/signal/sigelm.f	Sun Jun  3 18:52:29 2001
@@ -134,8 +134,18 @@
  22   continue
 c     rhs=4
       ilinc=iadr(lstk(top))
+      if (istk(ilinc).ne.1) then  !protect the 4th arg. (GA 2001) 
+         err=4
+         call error(53)
+         return
+      endif
       linc=sadr(ilinc+4)
       nspn=int(stk(linc))
+      if (nspn.eq.0) then  !protect the 4th arg. (GA 2001)
+         err=4
+         call error(36)
+         return
+      endif
       top=top-1
       iln=iadr(lstk(top))
       ln=sadr(iln+4)