diff -r 9ded2433dc2c Lib/secrets.py
--- a/Lib/secrets.py	Mon Nov 28 20:56:37 2016 +0200
+++ b/Lib/secrets.py	Tue Dec 27 18:28:24 2016 +0530
@@ -25,7 +25,9 @@
 choice = _sysrand.choice
 
 def randbelow(exclusive_upper_bound):
-    """Return a random int in the range [0, n)."""
+    """Return a random int in the range [0,n).  Raises ValueError if n <= 0."""
+    if exclusive_upper_bound <= 0:
+        raise ValueError("Upper bound must be positive.")
     return _sysrand._randbelow(exclusive_upper_bound)
 
 DEFAULT_ENTROPY = 32  # number of bytes to return by default
diff -r 9ded2433dc2c Lib/test/test_secrets.py
--- a/Lib/test/test_secrets.py	Mon Nov 28 20:56:37 2016 +0200
+++ b/Lib/test/test_secrets.py	Tue Dec 27 18:28:24 2016 +0530
@@ -70,6 +70,7 @@
         for i in range(2, 10):
             self.assertIn(secrets.randbelow(i), range(i))
         self.assertRaises(ValueError, secrets.randbelow, 0)
+        self.assertRaises(ValueError, secrets.randbelow, -1)
 
 
 class Token_Tests(unittest.TestCase):