diff --git a/mm/sparse.c b/mm/sparse.c
index a9783ac..83b3bf6 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -626,7 +626,7 @@ void online_mem_sections(unsigned long start_pfn, unsigned long end_pfn)
 	unsigned long pfn;
 
 	for (pfn = start_pfn; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
-		unsigned long section_nr = pfn_to_section_nr(start_pfn);
+		unsigned long section_nr = pfn_to_section_nr(pfn);
 		struct mem_section *ms;
 
 		/* onlining code should never touch invalid ranges */