diff --git a/src/hb-ot-layout-common-private.hh b/src/hb-ot-layout-common-private.hh
index 2943a7f67..a3afb0839 100644
--- a/src/hb-ot-layout-common-private.hh
+++ b/src/hb-ot-layout-common-private.hh
@@ -558,7 +558,7 @@ struct ClassDefFormat1
   private:
   inline unsigned int get_class (hb_codepoint_t glyph_id) const
   {
-    if ((unsigned int) (glyph_id - startGlyph) < classValue.len)
+    if (unlikely ((unsigned int) (glyph_id - startGlyph) < classValue.len))
       return classValue[glyph_id - startGlyph];
     return 0;
   }