diff --git a/mrblib/init_mrblib.c b/mrblib/init_mrblib.c
index a845489f5..72355e3eb 100644
--- a/mrblib/init_mrblib.c
+++ b/mrblib/init_mrblib.c
@@ -11,7 +11,6 @@ mrb_init_mrblib(mrb_state *mrb)
 {
   int n = mrb_read_irep(mrb, mrblib_irep);
 
-  extern mrb_value mrb_top_self(mrb_state *mrb);
   mrb_run(mrb, mrb_proc_new(mrb, mrb->irep[n]), mrb_top_self(mrb));
 }