diff --git a/xen/Rules.mk b/xen/Rules.mk
index 5e0699e58b..1f171f88e2 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -223,6 +223,9 @@ $(filter %.init.o,$(obj-y) $(obj-bin-y) $(extra-y)): %.init.o: %.o FORCE
 quiet_cmd_cpp_i_c = CPP     $@
 cmd_cpp_i_c = $(CPP) $(call cpp_flags,$(c_flags)) -MQ $@ -o $@ $<
 
+quiet_cmd_cpp_i_S = CPP     $@
+cmd_cpp_i_S = $(CPP) $(call cpp_flags,$(a_flags)) -MQ $@ -o $@ $<
+
 quiet_cmd_cc_s_c = CC      $@
 cmd_cc_s_c = $(CC) $(filter-out -Wa$(comma)%,$(c_flags)) -S $< -o $@
 
@@ -232,6 +235,9 @@ cmd_cpp_s_S = $(CPP) $(call cpp_flags,$(a_flags)) -MQ $@ -o $@ $<
 %.i: %.c FORCE
 	$(call if_changed,cpp_i_c)
 
+%.i: %.S FORCE
+	$(call if_changed,cpp_i_S)
+
 %.s: %.c FORCE
 	$(call if_changed,cc_s_c)
 
diff --git a/xen/arch/x86/Makefile b/xen/arch/x86/Makefile
index 69b6cfaded..8e975f472d 100644
--- a/xen/arch/x86/Makefile
+++ b/xen/arch/x86/Makefile
@@ -273,7 +273,7 @@ efi/buildid.o efi/relocs-dummy.o: ;
 .PHONY: include
 include: $(BASEDIR)/include/asm-x86/asm-macros.h
 
-asm-macros.i: CFLAGS-y += -D__ASSEMBLY__ -P
+asm-macros.i: CFLAGS-y += -P
 
 $(BASEDIR)/include/asm-x86/asm-macros.h: asm-macros.i Makefile
 	echo '#if 0' >$@.new
diff --git a/xen/arch/x86/asm-macros.c b/xen/arch/x86/asm-macros.S
similarity index 100%
rename from xen/arch/x86/asm-macros.c
rename to xen/arch/x86/asm-macros.S