diff --git a/mm/sparse.c b/mm/sparse.c
index 2609aba..6b8b5e9 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -264,7 +264,11 @@ unsigned long __init node_memmap_size_bytes(int nid, unsigned long start_pfn,
  */
 static unsigned long sparse_encode_mem_map(struct page *mem_map, unsigned long pnum)
 {
-	return (unsigned long)(mem_map - (section_nr_to_pfn(pnum)));
+	unsigned long coded_mem_map =
+		(unsigned long)(mem_map - (section_nr_to_pfn(pnum)));
+	BUILD_BUG_ON(SECTION_MAP_LAST_BIT > (1UL<<PFN_SECTION_SHIFT));
+	BUG_ON(coded_mem_map & ~SECTION_MAP_MASK);
+	return coded_mem_map;
 }
 
 /*