diff --git a/lib/maple_tree.c b/lib/maple_tree.c
index 2f1f661157c9..47d0c95b9a01 100644
--- a/lib/maple_tree.c
+++ b/lib/maple_tree.c
@@ -3711,7 +3711,8 @@ static inline int mas_root_expand(struct ma_state *mas, void *entry)
 	mas->offset = slot;
 	pivots[slot] = mas->last;
 	if (mas->last != ULONG_MAX)
-		slot++;
+		pivots[++slot] = ULONG_MAX;
+
 	mas->depth = 1;
 	mas_set_height(mas);
 	ma_set_meta(node, maple_leaf_64, 0, slot);