diff --git a/include/linux/memory.h b/include/linux/memory.h
index 9a6bbf7..bb7384e 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -35,6 +35,7 @@
 };
 
 int arch_get_memory_phys_device(unsigned long start_pfn);
+unsigned long __weak memory_block_size_bytes(void);
 
 /* These states are exposed to userspace as text strings in sysfs */
 #define	MEM_ONLINE		(1<<0) /* exposed to userspace */