diff --git a/src/hb-vector.hh b/src/hb-vector.hh
index 0d98bd03e5ca7822f9cdd0c77cc5d0ab587ef290..b4175c55eb8bc6063f836651b0b2db68c6e45a88 100644
--- a/src/hb-vector.hh
+++ b/src/hb-vector.hh
@@ -89,6 +89,8 @@ struct hb_vector_t
     return arrayZ()[i];
   }
 
+  explicit_operator bool () const { return len; }
+
   hb_array_t<Type> as_array ()
   { return hb_array (arrayZ(), len); }
   hb_array_t<const Type> as_array () const