diff --git a/src/hb-map.hh b/src/hb-map.hh
index 40c232e..02d5406 100644
--- a/src/hb-map.hh
+++ b/src/hb-map.hh
@@ -166,7 +166,7 @@
   hb_codepoint_t operator [] (unsigned int key) const
   { return get (key); }
 
-  static const hb_codepoint_t INVALID = HB_MAP_VALUE_INVALID;
+  static constexpr hb_codepoint_t INVALID = HB_MAP_VALUE_INVALID;
 
   void clear ()
   {
diff --git a/src/hb-set.hh b/src/hb-set.hh
index 86a06fa..81b9064 100644
--- a/src/hb-set.hh
+++ b/src/hb-set.hh
@@ -666,7 +666,7 @@
     return INVALID;
   }
 
-  static const hb_codepoint_t INVALID = HB_SET_VALUE_INVALID;
+  static constexpr hb_codepoint_t INVALID = HB_SET_VALUE_INVALID;
 
   /*
    * Iterator implementation.