diff --git a/lib/ruby-sdl-ffi/sdl/mac.rb b/lib/ruby-sdl-ffi/sdl/mac.rb
index d4e8e74..5239e5a 100644
--- a/lib/ruby-sdl-ffi/sdl/mac.rb
+++ b/lib/ruby-sdl-ffi/sdl/mac.rb
@@ -158,7 +158,7 @@ module ObjC
       typedef :pointer, :sel
       typedef :pointer, :ivar
       typedef :pointer, :nsclass
-      callback :imp, [:id, :sel, :varargs], :id
+      callback :imp, [:id, :sel, :ivar], :id
 
 
       class NSObject < NiceFFI::OpaqueStruct