--- swig-4.0.1/Lib/ruby/rubytracking.swg.orig	2019-08-21 06:34:03.000000000 +0900
+++ swig-4.0.1/Lib/ruby/rubytracking.swg	2020-01-18 18:32:38.909450596 +0900
@@ -69,7 +69,7 @@ SWIGRUNTIME void SWIG_RubyInitializeTrac
     swig_ruby_trackings = (st_table*)NUM2SWIG(trackings_value);
   }
 
-  rb_define_virtual_variable("SWIG_TRACKINGS_COUNT", swig_ruby_trackings_count, NULL);
+  rb_define_virtual_variable("SWIG_TRACKINGS_COUNT", (rb_gvar_getter_t *)swig_ruby_trackings_count, (rb_gvar_setter_t *)NULL);
 }
 
 /* Add a Tracking from a C/C++ struct to a Ruby object */