--- a/build/moz.configure/init.configure
+++ b/build/moz.configure/init.configure
@@ -186,17 +186,17 @@ def virtualenv_python(env_python, build_
             python = mozconfig['vars']['modified']['PYTHON'][1]
 
     with LineIO(lambda l: log.error(l)) as out:
         verify_python_version(out)
     topsrcdir, topobjdir = build_env.topsrcdir, build_env.topobjdir
     if topobjdir.endswith('/js/src'):
         topobjdir = topobjdir[:-7]
 
-    with LineIO(lambda l: log.info(l)) as out:
+    with LineIO(lambda l: log.info(l), 'replace') as out:
         manager = VirtualenvManager(
             topsrcdir, topobjdir,
             os.path.join(topobjdir, '_virtualenv'), out,
             os.path.join(topsrcdir, 'build', 'virtualenv_packages.txt'))
 
     if python:
         # If we're not in the virtualenv, we need the which module for
         # find_program.

--- a/build/moz.configure/pkg.configure
+++ b/build/moz.configure/pkg.configure
@@ -69,17 +69,17 @@ def pkg_check_modules(var, package_desc,
             try:
                 subprocess.check_output([pkg_config, '--errors-to-stdout',
                                          '--print-errors', package_desc])
                 log.info("yes")
                 return True
             except subprocess.CalledProcessError as e:
                 log.info("no")
                 log_writer = log.warning if allow_missing else log.error
-                with LineIO(lambda l: log_writer(l)) as o:
+                with LineIO(lambda l: log_writer(l), 'replace') as o:
                     o.write(e.output)
                 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/util.configure
+++ b/build/moz.configure/util.configure
@@ -58,17 +58,17 @@ 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)) as o:
+                with LineIO(lambda l: log.debug('| %s', l), 'replace') as o:
                     o.write(out)
         if onerror:
             return onerror()
         die('Command `%s` failed with exit status %d.' %
             (quote(*args), retcode))
 
 
 @imports('os')

--- a/python/mozbuild/mozbuild/configure/util.py
+++ b/python/mozbuild/mozbuild/configure/util.py
@@ -189,24 +189,25 @@ class ConfigureOutputHandler(logging.Han
                 break
         self._keep_if_debug = self.KEEP
 
 
 class LineIO(object):
     '''File-like class that sends each line of the written data to a callback
     (without carriage returns).
     '''
-    def __init__(self, callback):
+    def __init__(self, callback, errors='strict'):
         self._callback = callback
         self._buf = ''
         self._encoding = getpreferredencoding()
+        self._errors = errors
 
     def write(self, buf):
         if self._encoding and isinstance(buf, str):
-            buf = buf.decode(self._encoding)
+            buf = buf.decode(self._encoding, self._errors)
         lines = buf.splitlines()
         if not lines:
             return
         if self._buf:
             lines[0] = self._buf + lines[0]
             self._buf = ''
         if not buf.endswith('\n'):
             self._buf = lines.pop()