--- a/python/mozlint/mozlint/cli.py
+++ b/python/mozlint/mozlint/cli.py
@@ -207,18 +207,30 @@ def run(paths, linters, formats, outgoin
         edit_issues(result)
         result = lint.roll(result.issues.keys())
 
     for formatter_name, path in formats:
         formatter = formatters.get(formatter_name)
 
         out = formatter(result)
         if out:
-            output_file = open(path, 'w') if path else sys.stdout
-            print(out, file=output_file)
+            fh = open(path, 'w') if path else sys.stdout
+
+            if not path and fh.encoding == 'ascii':
+                # If sys.stdout.encoding is ascii, printing output will fail
+                # due to the stylish formatter's use of unicode characters.
+                # Ideally the user should fix their environment by setting
+                # `LC_ALL=C.UTF-8` or similar. But this is a common enough
+                # problem that we help them out a little here by manually
+                # encoding and writing to the stdout buffer directly.
+                out += '\n'
+                fh.buffer.write(out.encode('utf-8', errors='replace'))
+                fh.buffer.flush()
+            else:
+                print(out, file=fh)
 
     return result.returncode
 
 
 if __name__ == '__main__':
     parser = MozlintParser()
     args = vars(parser.parse_args())
     sys.exit(run(**args))

--- a/python/mozlint/test/test_cli.py
+++ b/python/mozlint/test/test_cli.py
@@ -1,13 +1,15 @@
 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 import os
+import subprocess
+import sys
 from distutils.spawn import find_executable
 
 import mozunit
 import pytest
 
 from mozlint import cli
 
 here = os.path.abspath(os.path.dirname(__file__))
@@ -27,16 +29,27 @@ def run(parser, lintdir, files):
         args = args or []
         args.extend(files)
         lintargs = vars(parser.parse_args(args))
         lintargs['root'] = here
         return cli.run(**lintargs)
     return inner
 
 
+def test_cli_with_ascii_encoding(run, monkeypatch, capfd):
+    cmd = [sys.executable, 'runcli.py', '-l=string', '-f=stylish']
+    env = os.environ.copy()
+    env['PYTHONPATH'] = os.pathsep.join(sys.path)
+    env['PYTHONIOENCODING'] = 'ascii'
+    proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
+                            cwd=here, env=env, universal_newlines=True)
+    out = proc.communicate()[0]
+    assert 'Traceback' not in out
+
+
 def test_cli_run_with_fix(run, capfd):
     ret = run(['-f', 'json', '--fix', '--linter', 'external'])
     out, err = capfd.readouterr()
     assert ret == 0
     assert out.endswith('{}\n')
 
 
 @pytest.mark.skipif(not find_executable("echo"), reason="No `echo` executable found.")