diff --git a/detect_host_arch.py b/detect_host_arch.py
index 69c50f8703..5aec2c87df 100755
--- a/detect_host_arch.py
+++ b/detect_host_arch.py
@@ -9,7 +9,6 @@ from __future__ import print_function
 
 import platform
 import re
-import sys
 
 
 def HostArch():
diff --git a/tests/detect_host_arch_test.py b/tests/detect_host_arch_test.py
new file mode 100644
index 0000000000..ea6760f15d
--- /dev/null
+++ b/tests/detect_host_arch_test.py
@@ -0,0 +1,51 @@
+#!/usr/bin/env vpython3
+# Copyright 2019 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+import os
+import platform
+import sys
+import unittest
+
+sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
+
+import detect_host_arch
+from third_party import mock
+
+
+class DetectHostArchTest(unittest.TestCase):
+  def setUp(self):
+    super(DetectHostArchTest, self).setUp()
+    mock.patch('platform.machine').start()
+    mock.patch('platform.processor').start()
+    mock.patch('platform.architecture').start()
+    self.addCleanup(mock.patch.stopall)
+
+  def testHostArch(self):
+    test_cases = [
+      ('ia86', '', [''], 'x86'),
+      ('i86pc', '', [''], 'x86'),
+      ('x86_64', '', [''], 'x64'),
+      ('amd64', '', [''], 'x64'),
+      ('x86_64', '', ['32bit'], 'x86'),
+      ('amd64', '', ['32bit'], 'x86'),
+      ('arm', '', [''], 'arm'),
+      ('aarch64', '', [''], 'arm64'),
+      ('aarch64', '', ['32bit'], 'arm'),
+      ('mips64', '', [''], 'mips64'),
+      ('mips', '', [''], 'mips'),
+      ('ppc', '', [''], 'ppc'),
+      ('foo', 'powerpc', [''], 'ppc'),
+      ('s390', '', [''], 's390'),
+    ]
+
+    for machine, processor, arch, expected in test_cases:
+      platform.machine.return_value = machine
+      platform.processor.return_value = processor
+      platform.architecture.return_value = arch
+      self.assertEqual(expected, detect_host_arch.HostArch())
+
+
+if __name__ == '__main__':
+  unittest.main()