diff --git a/spec/bundler/support/builders.rb b/spec/bundler/support/builders.rb
index a187d2ae48..4d713d8708 100644
--- a/spec/bundler/support/builders.rb
+++ b/spec/bundler/support/builders.rb
@@ -497,7 +497,7 @@ module Spec
         write "ext/#{name}.c", <<-C
           #include "ruby.h"
 
-          void Init_#{name}_c() {
+          void Init_#{name}_c(void) {
             rb_define_module("#{Builders.constantize(name)}_IN_C");
           }
         C