diff --git a/nbval/kernel.py b/nbval/kernel.py
index b567a7f..ae381cf 100644
--- a/nbval/kernel.py
+++ b/nbval/kernel.py
@@ -7,6 +7,7 @@
 
 import os
 import logging
+import subprocess
 from pprint import pformat
 
 try:
@@ -85,7 +86,7 @@ def __init__(self, kernel_name, cwd=None, startup_timeout=60):
         self.km, self.kc = start_new_kernel(
             startup_timeout=startup_timeout,
             kernel_name=kernel_name,
-            stderr=open(os.devnull, 'w'),
+            stderr=subprocess.DEVNULL,
             cwd=cwd,
         )