diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
index 431a64f021c0ed7c5dc9a40c63096f99ba16d464..f6d4af8af8a8f5a491f837d9bb9c108313ecb7f0 100644
--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -104,7 +104,7 @@ static void grow_pgdat_span(struct pglist_data *pgdat,
 		pgdat->node_start_pfn = start_pfn;
 
 	if (end_pfn > old_pgdat_end_pfn)
-		pgdat->node_spanned_pages = end_pfn - pgdat->node_spanned_pages;
+		pgdat->node_spanned_pages = end_pfn - pgdat->node_start_pfn;
 }
 
 int online_pages(unsigned long pfn, unsigned long nr_pages)