diff --git a/ext/-test-/old_thread_select/extconf.rb b/ext/-test-/old_thread_select/extconf.rb
index 8b410218fa..730d9ec901 100644
--- a/ext/-test-/old_thread_select/extconf.rb
+++ b/ext/-test-/old_thread_select/extconf.rb
@@ -1 +1,4 @@
+$warnflags = "-Wno-deprecated-declarations"
+$warnflags = "" unless try_compile("", $warnflags)
+
 create_makefile("-test-/old_thread_select/old_thread_select")