diff --git a/bootstraptest/test_thread.rb b/bootstraptest/test_thread.rb
index 5fdb66bb68..a7478fcd2c 100644
--- a/bootstraptest/test_thread.rb
+++ b/bootstraptest/test_thread.rb
@@ -437,5 +437,9 @@ assert_finish 3, %q{
 }, '[ruby-core:23572]'
 
 assert_equal 'ok', %q{
-  Process.waitpid2(fork {sleep 1})[1].success? ? 'ok' : 'ng'
+  begin
+    Process.waitpid2(fork {sleep 1})[1].success? ? 'ok' : 'ng'
+  rescue NotImplementedError
+    'ok'
+  end
 }