diff --git a/include/asm-x86/setup.h b/include/asm-x86/setup.h
index 269ba7fe21d1134ab47985d6ad882780adfe6592..42bc62b4b70ceb831be1976f3aaf58596589e267 100644
--- a/include/asm-x86/setup.h
+++ b/include/asm-x86/setup.h
@@ -56,6 +56,8 @@ extern void probe_roms(void);
 extern unsigned long init_pg_tables_start;
 extern unsigned long init_pg_tables_end;
 
+#else
+void __init x86_64_start_kernel(char *real_mode);
 #endif /* __i386__ */
 #endif /* _SETUP */
 #endif /* __ASSEMBLY__ */