diff --git a/rogueviz/nilrider/nilrider.h b/rogueviz/nilrider/nilrider.h
index e70b4424..3e192f4a 100644
--- a/rogueviz/nilrider/nilrider.h
+++ b/rogueviz/nilrider/nilrider.h
@@ -81,6 +81,8 @@ struct goal {
   goalchecker check;
   };
 
+using surface_fun = std::function<ld(hyperpoint h)>;
+
 struct level {
   string name;
   char hotkey;
@@ -90,7 +92,7 @@ struct level {
   vector<string> map_tiles;
   ld startx, starty;
   ld scale;
-  std::function<ld(hyperpoint h)> surface;
+  surface_fun surface;
   
   bool initialized;