--- ./ppm/ppmmerge.c.orig	Mon Jan 31 11:44:31 1994
+++ ./ppm/ppmmerge.c	Sat Aug 12 23:51:35 1995
@@ -29,6 +29,10 @@
 	{
 	++argv;
 	--argc;
+	if(!*argv)	{
+		fprintf(stderr, "Usage: ppmmerge ppm_program_name [args ...]\n");
+		exit(1);
+		}
 	goto again;
 	}