diff --git a/arch/powerpc/Makefile b/arch/powerpc/Makefile
index ff3369b..c941d53 100644
--- a/arch/powerpc/Makefile
+++ b/arch/powerpc/Makefile
@@ -57,10 +57,15 @@
 endif
 endif
 
-# It seems there are times we use this Makefile without
-# including the config file, but this replicates the old behaviour
-ifeq ($(CONFIG_WORD_SIZE),)
-CONFIG_WORD_SIZE := 32
+# BITS is used as extension for files which are available in a 32 bit
+# and a 64 bit version to simplify shared Makefiles.
+# e.g.: obj-y += foo_$(BITS).o
+export BITS
+
+ifdef CONFIG_PPC64
+        BITS := 64
+else
+        BITS := 32
 endif
 
 UTS_MACHINE := $(OLDARCH)
@@ -88,10 +93,10 @@
 aflags-$(CONFIG_CPU_LITTLE_ENDIAN)	+= -mlittle-endian
 
 ifeq ($(HAS_BIARCH),y)
-override AS	+= -a$(CONFIG_WORD_SIZE)
-override LD	+= -m elf$(CONFIG_WORD_SIZE)$(LDEMULATION)
-override CC	+= -m$(CONFIG_WORD_SIZE)
-override AR	:= GNUTARGET=elf$(CONFIG_WORD_SIZE)-$(GNUTARGET) $(AR)
+override AS	+= -a$(BITS)
+override LD	+= -m elf$(BITS)$(LDEMULATION)
+override CC	+= -m$(BITS)
+override AR	:= GNUTARGET=elf$(BITS)-$(GNUTARGET) $(AR)
 endif
 
 LDFLAGS_vmlinux-y := -Bstatic
@@ -178,7 +183,7 @@
 KBUILD_CFLAGS	+= -pipe -Iarch/$(ARCH) $(CFLAGS-y)
 CPP		= $(CC) -E $(KBUILD_CFLAGS)
 
-CHECKFLAGS	+= -m$(CONFIG_WORD_SIZE) -D__powerpc__ -D__powerpc$(CONFIG_WORD_SIZE)__
+CHECKFLAGS	+= -m$(BITS) -D__powerpc__ -D__powerpc$(BITS)__
 ifdef CONFIG_CPU_BIG_ENDIAN
 CHECKFLAGS	+= -D__BIG_ENDIAN__
 else
@@ -233,7 +238,7 @@
 KBUILD_AFLAGS += $(aflags-y)
 KBUILD_CFLAGS += $(cflags-y)
 
-head-y				:= arch/powerpc/kernel/head_$(CONFIG_WORD_SIZE).o
+head-y				:= arch/powerpc/kernel/head_$(BITS).o
 head-$(CONFIG_8xx)		:= arch/powerpc/kernel/head_8xx.o
 head-$(CONFIG_40x)		:= arch/powerpc/kernel/head_40x.o
 head-$(CONFIG_44x)		:= arch/powerpc/kernel/head_44x.o