diff -r 9ded2433dc2c Lib/random.py
--- a/Lib/random.py	Mon Nov 28 20:56:37 2016 +0200
+++ b/Lib/random.py	Sat Dec 24 15:02:34 2016 +0530
@@ -221,8 +221,9 @@
 
     def _randbelow(self, n, int=int, maxsize=1<<BPF, type=type,
                    Method=_MethodType, BuiltinMethod=_BuiltinMethodType):
-        "Return a random int in the range [0,n).  Raises ValueError if n==0."
-
+        "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.")
         random = self.random
         getrandbits = self.getrandbits
         # Only call self.getrandbits if the original random() builtin method
diff -r 9ded2433dc2c Lib/test/test_random.py
--- a/Lib/test/test_random.py	Mon Nov 28 20:56:37 2016 +0200
+++ b/Lib/test/test_random.py	Sat Dec 24 15:02:34 2016 +0530
@@ -618,6 +618,14 @@
         random_mock.side_effect = [limit + epsilon, limit - epsilon]
         self.gen._randbelow(n, maxsize = maxsize)
 
+    def test_randbelow_random_equals_zero(self):
+        with self.assertRaises(ValueError):
+            self.gen._randbelow(0)
+
+    def test_randbelow_random_less_than_zero(self):
+        with self.assertRaises(ValueError):
+            self.gen._randbelow(-1)
+
     def test_randrange_bug_1590891(self):
         start = 1000000000000
         stop = -100000000000000000000