diff --git a/ext/visibility_monitor_c/ext.c b/ext/visibility_monitor_c/ext.c
index 3964e7b..7a95a87 100644
--- a/ext/visibility_monitor_c/ext.c
+++ b/ext/visibility_monitor_c/ext.c
@@ -36,7 +36,7 @@ static VALUE monitor_set_visibility_placeholder(VALUE mod, VALUE method_name, VA
     return Qnil;
 }
 
-void Init_visibility_monitor_c() {
+void Init_visibility_monitor_c(void) {
     VALUE mVisibilityMonitor = rb_define_module("VisibilityMonitor");
 
     rb_define_method(mVisibilityMonitor, "public", monitor_public, -1);