--- arch/powerpc/Makefile.orig	2006-08-05 14:22:50.000000000 -0400
+++ arch/powerpc/Makefile	2006-08-05 14:22:35.000000000 -0400
@@ -34,6 +34,13 @@
 export CROSS32CC CROSS32AS CROSS32LD CROSS32OBJCOPY
 
 KBUILD_DEFCONFIG := $(shell uname -m)_defconfig
+ifeq ($(wildcard $(srctree)/arch/powerpc/configs/$(KBUILD_DEFCONFIG)),)
+ifeq ($(CONFIG_PPC64),y)
+KBUILD_DEFCONFIG := ppc64_defconfig
+else
+KBUILD_DEFCONFIG := pmac32_defconfig
+endif
+endif
 
 ifeq ($(CONFIG_PPC64),y)
 OLDARCH	:= ppc64