diff --git a/src/ecdsa/numbertheory.py b/src/ecdsa/numbertheory.py
index c8f7a33c..05aaa984 100644
--- a/src/ecdsa/numbertheory.py
+++ b/src/ecdsa/numbertheory.py
@@ -225,11 +225,14 @@ def inverse_mod(a, m):
     return ud + m
 
 
-def gcd2(a, b):
-  """Greatest common divisor using Euclid's algorithm."""
-  while a:
-    a, b = b % a, a
-  return b
+try:
+    gcd2 = math.gcd
+except AttributeError:
+    def gcd2(a, b):
+        """Greatest common divisor using Euclid's algorithm."""
+        while a:
+            a, b = b % a, a
+        return b
 
 
 def gcd(*a):
@@ -567,4 +570,3 @@ def next_prime(starting_value):
                1171, 1181, 1187, 1193, 1201, 1213, 1217, 1223, 1229]
 
 miller_rabin_test_count = 0
-