diff --git a/src/hb-map-private.hh b/src/hb-map-private.hh
index ef2ee4667..cdd90c5c9 100644
--- a/src/hb-map-private.hh
+++ b/src/hb-map-private.hh
@@ -90,7 +90,7 @@ struct hb_map_t
   {
     if (unlikely (in_error)) return false;
 
-    unsigned int power = _hb_bit_storage (population * 2 + 8) - 1;
+    unsigned int power = _hb_bit_storage (population * 2 + 8);
     unsigned int new_size = 1u << power;
     item_t *new_items = (item_t *) malloc ((size_t) new_size * sizeof (item_t));
     if (unlikely (!new_items))