--- a/python/mozbuild/mozbuild/test/configure/common.py
+++ b/python/mozbuild/mozbuild/test/configure/common.py
@@ -100,16 +100,17 @@ class ConfigureTestSandbox(ConfigureSand
         if what == 'subprocess.Popen':
             return self.Popen
 
         if what == 'subprocess':
             return ReadOnlyNamespace(
                 CalledProcessError=subprocess.CalledProcessError,
                 check_output=self.check_output,
                 PIPE=subprocess.PIPE,
+                STDOUT=subprocess.STDOUT,
                 Popen=self.Popen,
             )
 
         if what == 'os.environ':
             return self._environ
 
         return super(ConfigureTestSandbox, self)._get_one_import(what)
 
@@ -133,18 +134,18 @@ class ConfigureTestSandbox(ConfigureSand
             def communicate(self, stdin=None):
                 return stdout, stderr
 
             def wait(self):
                 return retcode
 
         return Process()
 
-    def check_output(self, args):
-        proc = self.Popen(args)
+    def check_output(self, args, **kwargs):
+        proc = self.Popen(args, **kwargs)
         stdout, stderr = proc.communicate()
         retcode = proc.wait()
         if retcode:
             raise subprocess.CalledProcessError(retcode, args, stdout)
         return stdout
 
     def shell(self, stdin, args):
         script = mozpath.abspath(args[0])