Index: suckless-tools-39/slock/Makefile
===================================================================
--- suckless-tools-39.orig/slock/Makefile	2012-01-23 11:59:50.186494839 +0100
+++ suckless-tools-39/slock/Makefile	2012-01-23 11:59:54.258583809 +0100
@@ -41,7 +41,8 @@
 	@mkdir -p ${DESTDIR}${PREFIX}/bin
 	@cp -f slock ${DESTDIR}${PREFIX}/bin
 	@chmod 755 ${DESTDIR}${PREFIX}/bin/slock
-	@chmod u+s ${DESTDIR}${PREFIX}/bin/slock
+	@chgrp shadow ${DESTDIR}${PREFIX}/bin/slock
+	@chmod g+s ${DESTDIR}${PREFIX}/bin/slock
 
 uninstall:
 	@echo removing executable file from ${DESTDIR}${PREFIX}/bin
Index: suckless-tools-39/slock/slock.c
===================================================================
--- suckless-tools-39.orig/slock/slock.c	2008-07-29 20:22:46.000000000 +0200
+++ suckless-tools-39/slock/slock.c	2012-01-23 13:03:08.275556534 +0100
@@ -38,16 +38,17 @@
 	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;
-
-#if HAVE_SHADOW_H
+#ifdef HAVE_SHADOW_H
 	{
 		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;
 	}