diff --git a/src/hb-ot-layout-gsub-table.hh b/src/hb-ot-layout-gsub-table.hh
index a6cc1a230..84e1b1578 100644
--- a/src/hb-ot-layout-gsub-table.hh
+++ b/src/hb-ot-layout-gsub-table.hh
@@ -248,7 +248,7 @@ struct SingleSubst
     if (unlikely (!c->extend_min (u.format))) return_trace (false);
     unsigned format = 2;
     unsigned delta = 0;
-    if (glyphs.len ())
+    if (glyphs)
     {
       format = 1;
       auto get_delta = [=] (hb_codepoint_pair_t _) {