diff --git a/Lib/subprocess.py b/Lib/subprocess.py
--- a/Lib/subprocess.py
+++ b/Lib/subprocess.py
@@ -510,16 +510,16 @@ def check_output(*popenargs, timeout=Non
     """
     if 'stdout' in kwargs:
         raise ValueError('stdout argument not allowed, it will be overridden.')
-    process = Popen(*popenargs, stdout=PIPE, **kwargs)
-    try:
-        output, unused_err = process.communicate(timeout=timeout)
-    except TimeoutExpired:
-        process.kill()
-        output, unused_err = process.communicate()
-        raise TimeoutExpired(process.args, timeout, output=output)
-    retcode = process.poll()
-    if retcode:
-        raise CalledProcessError(retcode, process.args, output=output)
+    with Popen(*popenargs, stdout=PIPE, **kwargs) as process:
+        try:
+            output, unused_err = process.communicate(timeout=timeout)
+        except TimeoutExpired:
+            process.kill()
+            output, unused_err = process.communicate()
+            raise TimeoutExpired(process.args, timeout, output=output)
+        retcode = process.poll()
+        if retcode:
+            raise CalledProcessError(retcode, process.args, output=output)
     return output