diff --git a/docs/hazmat/primitives/mac/cmac.rst b/docs/hazmat/primitives/mac/cmac.rst
index c7eabd9d953f..f5e8b59c0f4d 100644
--- a/docs/hazmat/primitives/mac/cmac.rst
+++ b/docs/hazmat/primitives/mac/cmac.rst
@@ -28,6 +28,7 @@ A subset of CMAC with the AES-128 algorithm is described in :rfc:`4493`.
 
         >>> from cryptography.hazmat.primitives import cmac
         >>> from cryptography.hazmat.primitives.ciphers import algorithms
+        >>> key = b"\x00" * 16 # A real key should come from os.urandom(16)
         >>> c = cmac.CMAC(algorithms.AES(key))
         >>> c.update(b"message to authenticate")
         >>> c.finalize()
diff --git a/docs/hazmat/primitives/mac/poly1305.rst b/docs/hazmat/primitives/mac/poly1305.rst
index e3240f5baccf..cc7f9e2b7a58 100644
--- a/docs/hazmat/primitives/mac/poly1305.rst
+++ b/docs/hazmat/primitives/mac/poly1305.rst
@@ -31,6 +31,7 @@ messages allows an attacker to forge tags. Poly1305 is described in
     .. doctest::
 
         >>> from cryptography.hazmat.primitives import poly1305
+        >>> key = b"\x01" * 32 # A real key should come from os.urandom(32)
         >>> p = poly1305.Poly1305(key)
         >>> p.update(b"message to authenticate")
         >>> p.finalize()