diff --git a/arch/um/Makefile-x86_64 b/arch/um/Makefile-x86_64
index 9558a7cf34d599f8eda369838ffda69bba6ec646..11154b6773ec230302341d8889e79601677b47c1 100644
--- a/arch/um/Makefile-x86_64
+++ b/arch/um/Makefile-x86_64
@@ -4,10 +4,13 @@
 core-y += arch/um/sys-x86_64/
 START := 0x60000000
 
+_extra_flags_ = -fno-builtin -m64 -mcmodel=kernel
+
 #We #undef __x86_64__ for kernelspace, not for userspace where
 #it's needed for headers to work!
-CFLAGS += -U__$(SUBARCH)__ -fno-builtin -m64
-USER_CFLAGS += -fno-builtin -m64
+CFLAGS += -U__$(SUBARCH)__ $(_extra_flags_)
+USER_CFLAGS += $(_extra_flags_)
+
 CHECKFLAGS  += -m64
 AFLAGS += -m64
 LDFLAGS += -m elf_x86_64