diff --git a/sys/arch/sparc/sparc/machdep.c b/sys/arch/sparc/sparc/machdep.c
index f83a697cbda0..9fb04570c345 100644
--- a/sys/arch/sparc/sparc/machdep.c
+++ b/sys/arch/sparc/sparc/machdep.c
@@ -1,4 +1,4 @@
-/*	$NetBSD: machdep.c,v 1.219 2003/01/13 16:59:17 pk Exp $ */
+/*	$NetBSD: machdep.c,v 1.220 2003/01/16 11:33:21 pk Exp $ */
 
 /*-
  * Copyright (c) 1996, 1997, 1998 The NetBSD Foundation, Inc.
@@ -739,6 +739,7 @@ cpu_reboot(howto, user_boot_string)
 	char *user_boot_string;
 {
 	int i;
+	char opts[4];
 	static char str[128];
 
 	/* If system is cold, just halt. */
@@ -828,26 +829,24 @@ cpu_reboot(howto, user_boot_string)
 	}
 
 	printf("rebooting\n\n");
+
+	i = 1;
+	if (howto & RB_SINGLE)
+		opts[i++] = 's';
+	if (howto & RB_KDB)
+		opts[i++] = 'd';
+	opts[i] = '\0';
+	opts[0] = (i > 1) ? '-' : '\0';
+
 	if (user_boot_string && *user_boot_string) {
 		i = strlen(user_boot_string);
-		if (i > sizeof(str))
+		if (i > sizeof(str) - sizeof(opts) - 1)
 			prom_boot(user_boot_string);	/* XXX */
 		bcopy(user_boot_string, str, i);
-	} else {
-		i = 1;
-		str[0] = '\0';
+		if (opts[0] != '\0')
+			str[i] = ' ';
 	}
-
-	if (howto & RB_SINGLE)
-		str[i++] = 's';
-	if (howto & RB_KDB)
-		str[i++] = 'd';
-	if (i > 1) {
-		if (str[0] == '\0')
-			str[0] = '-';
-		str[i] = 0;
-	} else
-		str[0] = 0;
+	strcat(str, opts);
 	prom_boot(str);
 	/*NOTREACHED*/
 }