diff --git a/xen/arch/x86/boot/Makefile b/xen/arch/x86/boot/Makefile
index 13f4a66c92..5fdb5aee7b 100644
--- a/xen/arch/x86/boot/Makefile
+++ b/xen/arch/x86/boot/Makefile
@@ -1,8 +1,8 @@
 obj-bin-y += head.o
 
+RELOC_DEPS = $(BASEDIR)/include/asm-x86/config.h $(BASEDIR)/include/xen/multiboot.h
+
 head.o: reloc.S
 
-%.S: %.c
-	$(MAKE) -f build32.mk $@
-
-reloc.S: head.S
+reloc.S: reloc.c $(RELOC_DEPS)
+	$(MAKE) -f build32.mk $@ RELOC_DEPS="$(RELOC_DEPS)"
diff --git a/xen/arch/x86/boot/build32.mk b/xen/arch/x86/boot/build32.mk
index a36f62064e..c208249ca8 100644
--- a/xen/arch/x86/boot/build32.mk
+++ b/xen/arch/x86/boot/build32.mk
@@ -30,5 +30,6 @@ CFLAGS := $(filter-out -flto,$(CFLAGS))
 			esac; \
 		done
 
-reloc.o: $(BASEDIR)/include/asm-x86/config.h
+reloc.o: reloc.c $(RELOC_DEPS)
+
 .PRECIOUS: %.bin %.lnk