diff --git a/test/stdlib/IO_test.rb b/test/stdlib/IO_test.rb
index 2e40ece55..962333e0f 100644
--- a/test/stdlib/IO_test.rb
+++ b/test/stdlib/IO_test.rb
@@ -35,19 +35,16 @@ def test_binwrite
 
   def test_open
     Dir.mktmpdir do |dir|
-      fd = IO.sysopen(File.expand_path(__FILE__))
-
       assert_send_type "(Integer) -> IO",
-                       IO, :open, fd
+                       IO, :open, IO.sysopen(File.expand_path(__FILE__))
       assert_send_type "(ToInt, String) -> IO",
-                       IO, :open, ToInt.new(fd), "r"
+                       IO, :open, ToInt.new(IO.sysopen(File.expand_path(__FILE__))), "r"
       assert_send_type "(Integer) { (IO) -> Integer } -> Integer",
-                       IO, :open, fd do |io| io.read.size end
+                       IO, :open, IO.sysopen(File.expand_path(__FILE__)), &proc {|io| io.read.size }
 
-      fd = IO.sysopen(File.expand_path(__FILE__))
       assert_send_type(
         "(ToInt, path: String) -> IO",
-        IO, :open, ToInt.new(fd), path: "<<TEST>>"
+        IO, :open, ToInt.new(IO.sysopen(File.expand_path(__FILE__))), path: "<<TEST>>"
       )
     end
   end