diff --git a/src/cryptography/x509.py b/src/cryptography/x509.py
index 1635a51..e6d19ae 100644
--- a/src/cryptography/x509.py
+++ b/src/cryptography/x509.py
@@ -1172,7 +1172,6 @@
         """
         Serializes the certificate to PEM or DER format.
         """
-        pass
 
 
 @six.add_metaclass(abc.ABCMeta)