diff --git a/ext/etc/extconf.rb b/ext/etc/extconf.rb
index 3d7ccea..497303a 100644
--- a/ext/etc/extconf.rb
+++ b/ext/etc/extconf.rb
@@ -60,7 +60,7 @@
 # TODO: remove when dropping 2.7 support, as exported since 3.0
 have_func('rb_deprecate_constant(Qnil, "None")')
 
-have_func("rb_io_descriptor")
+have_func("rb_io_descriptor", "ruby/io.h")
 
 $distcleanfiles << "constdefs.h"