--- slock.c.orig	2012-01-24 10:57:52.751270668 +0100
+++ slock.c	2012-01-24 10:59:00.616019472 +0100
@@ -38,9 +38,9 @@
 	const char *rval;
 	struct passwd *pw;
 
-	if(geteuid() != 0)
-		die("slock: cannot retrieve password entry (make sure to suid slock)\n");
 	pw = getpwuid(getuid());
+	if(!pw)
+		die("slock: cannot retrieve password entry (may you need to suid or sgid slock?)\n");
 	endpwent();
 	rval =  pw->pw_passwd;
 
@@ -48,6 +48,8 @@
 	{
 		struct spwd *sp;
 		sp = getspnam(getenv("USER"));
+		if(!sp)
+			die("slock: cannot retrieve shadow entry (may you need to suid or sgid slock?)\n");
 		endspent();
 		rval = sp->sp_pwdp;
 	}