diff --git a/include/linux/memory.h b/include/linux/memory.h
index 9a6bbf76452d16a89d53485225901f7af80823c1..bb7384e3c3d89fbd1a36504587035cc0325953e7 100644
--- a/include/linux/memory.h
+++ b/include/linux/memory.h
@@ -35,6 +35,7 @@ struct memory_block {
 };
 
 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 */