diff --git a/Lib/test/test_float.py b/Lib/test/test_float.py
index e6779c4..5bf1d31 100644
--- a/Lib/test/test_float.py
+++ b/Lib/test/test_float.py
@@ -8,6 +8,7 @@
 import random
 import fractions
 import sys
+import time
 
 INF = float("inf")
 NAN = float("nan")
@@ -164,6 +165,11 @@
         self.assertAlmostEqual(float(FooUnicode('8')), 9.)
         self.assertAlmostEqual(float(FooStr('8')), 9.)
 
+        class Foo5:
+            def __float__(self):
+                return ""
+        self.assertRaises(TypeError, time.sleep, Foo5())
+
     def test_is_integer(self):
         self.assertFalse((1.1).is_integer())
         self.assertTrue((1.).is_integer())