diff --git a/src/hb-map.hh b/src/hb-map.hh
index 311e612a8..bb4a0eb5d 100644
--- a/src/hb-map.hh
+++ b/src/hb-map.hh
@@ -39,6 +39,9 @@ template <typename K, typename V,
 	  V vINVALID = hb_is_pointer (V) ? 0 : std::is_signed<V>::value ? hb_int_min (V) : (V) -1>
 struct hb_hashmap_t
 {
+  static constexpr K INVALID_KEY   = kINVALID;
+  static constexpr V INVALID_VALUE = vINVALID;
+
   hb_hashmap_t ()  { init (); }
   ~hb_hashmap_t () { fini (); }