diff --git a/arch/x86/include/asm/memtype.h b/arch/x86/include/asm/memtype.h
index ec18e38ae391..9c2447b3555d 100644
--- a/arch/x86/include/asm/memtype.h
+++ b/arch/x86/include/asm/memtype.h
@@ -5,8 +5,8 @@
 #include <linux/types.h>
 #include <asm/pgtable_types.h>
 
-bool pat_enabled(void);
-void pat_disable(const char *reason);
+extern bool pat_enabled(void);
+extern void pat_disable(const char *reason);
 extern void pat_init(void);
 extern void init_cache_modes(void);
 
@@ -17,11 +17,11 @@ extern int memtype_free(u64 start, u64 end);
 extern int memtype_kernel_map_sync(u64 base, unsigned long size,
 		enum page_cache_mode pcm);
 
-int memtype_reserve_io(resource_size_t start, resource_size_t end,
+extern int memtype_reserve_io(resource_size_t start, resource_size_t end,
 			enum page_cache_mode *pcm);
 
-void memtype_free_io(resource_size_t start, resource_size_t end);
+extern void memtype_free_io(resource_size_t start, resource_size_t end);
 
-bool pat_pfn_immune_to_uc_mtrr(unsigned long pfn);
+extern bool pat_pfn_immune_to_uc_mtrr(unsigned long pfn);
 
 #endif /* _ASM_X86_MEMTYPE_H */