diff --git a/swift/common/utils.py b/swift/common/utils.py
index e4c2bccf3c..13dd314514 100644
--- a/swift/common/utils.py
+++ b/swift/common/utils.py
@@ -4972,11 +4972,15 @@ except TypeError:
 
 class ShardRangeOuterBound(object):
     """
-    A custom singleton type used for the outer bounds of ShardRanges.
+    A custom singleton type to be subclassed for the outer bounds of
+    ShardRanges.
     """
     _singleton = None
 
     def __new__(cls):
+        if cls is ShardRangeOuterBound:
+            raise TypeError('ShardRangeOuterBound is an abstract class; '
+                            'only subclasses should be instantiated')
         if cls._singleton is None:
             cls._singleton = super(ShardRangeOuterBound, cls).__new__(cls)
         return cls._singleton
diff --git a/test/unit/common/test_utils.py b/test/unit/common/test_utils.py
index 7bcf9f996d..cf01ce90b3 100644
--- a/test/unit/common/test_utils.py
+++ b/test/unit/common/test_utils.py
@@ -7732,6 +7732,9 @@ class TestShardRange(unittest.TestCase):
         self.ts_iter = make_timestamp_iter()
 
     def test_min_max_bounds(self):
+        with self.assertRaises(TypeError):
+            utils.ShardRangeOuterBound()
+
         # max
         self.assertEqual(utils.ShardRange.MAX, utils.ShardRange.MAX)
         self.assertFalse(utils.ShardRange.MAX > utils.ShardRange.MAX)