diff --git a/maths/miller_rabin.py b/maths/miller_rabin.py
index d35e54858..b4dfed129 100644
--- a/maths/miller_rabin.py
+++ b/maths/miller_rabin.py
@@ -8,9 +8,9 @@ from .binary_exp_mod import bin_exp_mod
 # if it's not a prime, the chance of it returning true is at most 1/4**prec
 def is_prime_big(n, prec=1000):
     """
-    >>> from maths.prime_check import prime_check
-    >>> # all(is_prime_big(i) == prime_check(i) for i in range(1000))  # 3.45s
-    >>> all(is_prime_big(i) == prime_check(i) for i in range(256))
+    >>> from maths.prime_check import is_prime
+    >>> # all(is_prime_big(i) == is_prime(i) for i in range(1000))  # 3.45s
+    >>> all(is_prime_big(i) == is_prime(i) for i in range(256))
     True
     """
     if n < 2:
diff --git a/maths/prime_check.py b/maths/prime_check.py
index 6af5a75c2..80ab8bc5d 100644
--- a/maths/prime_check.py
+++ b/maths/prime_check.py
@@ -62,10 +62,8 @@ class Test(unittest.TestCase):
         self.assertTrue(is_prime(29))
 
     def test_not_primes(self):
-        self.assertFalse(
-            is_prime(-19),
-            "Negative numbers are excluded by definition of prime numbers.",
-        )
+        with self.assertRaises(AssertionError):
+            is_prime(-19)
         self.assertFalse(
             is_prime(0),
             "Zero doesn't have any positive factors, primes must have exactly two.",