--- a/build/moz.configure/pkg.configure
+++ b/build/moz.configure/pkg.configure
@@ -66,17 +66,17 @@ def pkg_check_modules(var, package_desc,
         log.info("checking for %s... " % package_desc)
         retcode, stdout, stderr = get_cmd_output(
             pkg_config, '--errors-to-stdout', '--print-errors', package_desc)
         if retcode == 0:
             log.info("yes")
             return True
         log.info("no")
         log_writer = log.warning if allow_missing else log.error
-        with LineIO(lambda l: log_writer(l), 'replace') as o:
+        with LineIO(lambda l: log_writer(l)) as o:
             o.write(stdout)
         if not allow_missing:
             sys.exit(1)
 
     @depends(pkg_config, package_desc, when=package)
     @checking('%s_CFLAGS' % var, callback=lambda t: ' '.join(t))
     def pkg_cflags(pkg_config, package_desc):
         flags = check_cmd_output(pkg_config, '--cflags', package_desc)

--- a/build/moz.configure/toolchain.configure
+++ b/build/moz.configure/toolchain.configure
@@ -598,30 +598,27 @@ def check_compiler(compiler, language, t
         target_os=info.os,
         flags=flags,
     )
 
 
 @imports(_from='__builtin__', _import='open')
 @imports('json')
 @imports('os')
-@imports(_from='mozbuild.util', _import='system_encoding')
 def get_vc_paths(topsrcdir):
     def vswhere(args):
         program_files = (os.environ.get('PROGRAMFILES(X86)') or
                          os.environ.get('PROGRAMFILES'))
         if not program_files:
             return []
         vswhere = os.path.join(program_files, 'Microsoft Visual Studio',
                                'Installer', 'vswhere.exe')
         if not os.path.exists(vswhere):
             return []
-        return json.loads(
-            check_cmd_output(vswhere, '-format', 'json', *args)
-            .decode(system_encoding, 'replace'))
+        return json.loads(check_cmd_output(vswhere, '-format', 'json', *args))
 
     for install in vswhere(['-products', '*', '-requires', 'Microsoft.VisualStudio.Component.VC.Tools.x86.x64']):
         path = install['installationPath']
         tools_version = open(os.path.join(
             path, r'VC\Auxiliary\Build\Microsoft.VCToolsVersion.default.txt'), 'rb').read().strip()
         tools_path = os.path.join(
             path, r'VC\Tools\MSVC', tools_version)
         yield (Version(install['installationVersion']), tools_path)

--- a/build/moz.configure/util.configure
+++ b/build/moz.configure/util.configure
@@ -21,16 +21,17 @@ def configure_error(message):
 
 
 # A wrapper to obtain a process' output and return code.
 # Returns a tuple (retcode, stdout, stderr).
 @imports('os')
 @imports(_from='__builtin__', _import='unicode')
 @imports('subprocess')
 @imports(_from='mozbuild.shellutil', _import='quote')
+@imports(_from='mozbuild.util', _import='system_encoding')
 def get_cmd_output(*args, **kwargs):
     # subprocess on older Pythons can't handle unicode keys or values in
     # environment dicts. Normalize automagically so callers don't have to
     # deal with this.
     if 'env' in kwargs:
         normalized_env = {}
         for k, v in kwargs['env'].items():
             if isinstance(k, unicode):
@@ -48,16 +49,18 @@ def get_cmd_output(*args, **kwargs):
                             stderr=subprocess.PIPE,
                             # On Python 2 on Windows, close_fds prevents the
                             # process from inheriting stdout/stderr.
                             # Elsewhere, it simply prevents it from inheriting
                             # extra file descriptors, which is what we want.
                             close_fds=os.name != 'nt',
                             **kwargs)
     stdout, stderr = proc.communicate()
+    stdout = stdout.decode(system_encoding, 'replace')
+    stderr = stderr.decode(system_encoding, 'replace')
     return proc.wait(), stdout, stderr
 
 
 # A wrapper to obtain a process' output that returns the output generated
 # by running the given command if it exits normally, and streams that
 # output to log.debug and calls die or the given error callback if it
 # does not.
 @imports(_from='mozbuild.configure.util', _import='LineIO')
@@ -70,17 +73,17 @@ def check_cmd_output(*args, **kwargs):
         if retcode == 0:
             return stdout
 
         log.debug('The command returned non-zero exit status %d.',
                   retcode)
         for out, desc in ((stdout, 'output'), (stderr, 'error output')):
             if out:
                 log.debug('Its %s was:', desc)
-                with LineIO(lambda l: log.debug('| %s', l), 'replace') as o:
+                with LineIO(lambda l: log.debug('| %s', l)) as o:
                     o.write(out)
         if onerror:
             return onerror()
         die('Command `%s` failed with exit status %d.' %
             (quote(*args), retcode))
 
 
 @imports('os')