diff --git a/src/hb-ot-layout.hh b/src/hb-ot-layout.hh
index fcc0998..02c8c7b 100644
--- a/src/hb-ot-layout.hh
+++ b/src/hb-ot-layout.hh
@@ -34,6 +34,7 @@
 #include "hb-font.hh"
 #include "hb-buffer.hh"
 #include "hb-open-type.hh"
+#include "hb-set-digest.hh"
 
 
 /* Private API corresponding to hb-ot-layout.h: */
@@ -86,7 +87,22 @@
 			       hb_buffer_t  *buffer);
 
 
-struct hb_ot_layout_lookup_accelerator_t;
+struct hb_ot_layout_lookup_accelerator_t
+{
+  template <typename TLookup>
+  inline void init (const TLookup &lookup)
+  {
+    digest.init ();
+    lookup.add_coverage (&digest);
+  }
+  inline void fini (void) {}
+
+  inline bool may_have (hb_codepoint_t g) const
+  { return digest.may_have (g); }
+
+  private:
+  hb_set_digest_t digest;
+};
 
 namespace OT {
   struct hb_ot_apply_context_t;