diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index b27e8d71cda3..c1ccc89845f4 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1387,7 +1387,7 @@ static int get_nodes(nodemask_t *nodes, const unsigned long __user *nmask,
 		unsigned long bits = min_t(unsigned long, maxnode, BITS_PER_LONG);
 		unsigned long t;
 
-		if (get_bitmap(&t, &nmask[maxnode / BITS_PER_LONG], bits))
+		if (get_bitmap(&t, &nmask[(maxnode - 1) / BITS_PER_LONG], bits))
 			return -EFAULT;
 
 		if (maxnode - bits >= MAX_NUMNODES) {