diff --git a/src/hb-ot-layout-common-private.hh b/src/hb-ot-layout-common-private.hh
index d3c5bef..72b50c0 100644
--- a/src/hb-ot-layout-common-private.hh
+++ b/src/hb-ot-layout-common-private.hh
@@ -533,7 +533,7 @@
 
 struct ClassDef
 {
-  inline unsigned int operator() (hb_codepoint_t glyph_id) const { return get_class (glyph_id); }
+  inline hb_ot_layout_class_t operator() (hb_codepoint_t glyph_id) const { return get_class (glyph_id); }
 
   inline hb_ot_layout_class_t get_class (hb_codepoint_t glyph_id) const
   {