diff --git a/ansible_mitogen/helpers.py b/ansible_mitogen/helpers.py
index a4ba59f6..b1dcfe8f 100644
--- a/ansible_mitogen/helpers.py
+++ b/ansible_mitogen/helpers.py
@@ -190,9 +190,6 @@ CHMOD_BITS = {
     }
 }
 
-def or_(it):
-    return reduce(operator.or_, it, 0)
-
 
 def apply_mode_spec(spec, mode):
     for clause in spec.split(','):
@@ -202,7 +199,7 @@ def apply_mode_spec(spec, mode):
             mask = CHMOD_MASKS[ch]
             bits = CHMOD_BITS[ch]
             cur_perm_bits = mode & mask
-            new_perm_bits = or_(bits[p] for p in perms)
+            new_perm_bits = reduce(operator.or_, (bits[p] for p in perms), 0)
             mode &= ~mask
             if op == '=':
                 mode |= new_perm_bits
diff --git a/tests/ansible_helpers_test.py b/tests/ansible_helpers_test.py
new file mode 100644
index 00000000..b582466a
--- /dev/null
+++ b/tests/ansible_helpers_test.py
@@ -0,0 +1,20 @@
+
+import unittest2
+
+import ansible_mitogen.helpers
+import testlib
+
+
+class ApplyModeSpecTest(unittest2.TestCase):
+    func = staticmethod(ansible_mitogen.apply_mode_spec)
+
+    def test_simple(self):
+        spec = 'u+rwx,go=x'
+        self.assertEquals(0711, self.func(spec, 0))
+
+        spec = 'g-rw'
+        self.assertEquals(0717, self.func(spec, 0777))
+
+
+if __name__ == '__main__':
+    unittest2.main()