Index: linux/arch/powerpc/kernel/prom_init.c
===================================================================
--- linux/arch/powerpc/kernel/prom_init.c	(revision 3)
+++ linux/arch/powerpc/kernel/prom_init.c	(working copy)
@@ -559,7 +559,7 @@
 	if ((long)_prom->chosen > 0)
 		l = prom_getprop(_prom->chosen, "bootargs", p, COMMAND_LINE_SIZE-1);
 #ifdef CONFIG_CMDLINE
-	if (l == 0) /* dbl check */
+	if (l == 0 || p[0] == '\0') /* dbl check */
 		strlcpy(RELOC(prom_cmd_line),
 			RELOC(CONFIG_CMDLINE), sizeof(prom_cmd_line));
 #endif /* CONFIG_CMDLINE */