diff --git a/io.c b/io.c
index cd8dcb07a3..ed7d28d9c9 100644
--- a/io.c
+++ b/io.c
@@ -10872,7 +10872,6 @@ rb_io_set_encoding(int argc, VALUE *argv, VALUE io)
 void
 rb_stdio_set_default_encoding(void)
 {
-    extern VALUE rb_stdin, rb_stdout, rb_stderr;
     VALUE val = Qnil;
 
     rb_io_set_encoding(1, &val, rb_stdin);