diff --git a/docs/development/test-vectors.rst b/docs/development/test-vectors.rst
index bc171b2..ac667bb 100644
--- a/docs/development/test-vectors.rst
+++ b/docs/development/test-vectors.rst
@@ -204,6 +204,9 @@
   name constraints extension with permitted elements.
 * ``nc_excluded.pem`` - An RSA 2048 bit self-signed certificate containing a
   name constraints extension with excluded elements.
+* ``nc_invalid_ip_netmask.pem`` - An RSA 2048 bit self-signed certificate
+  containing a name constraints extension with a permitted element that has an
+  ``IPv6`` IP and an invalid network mask.
 * ``cp_user_notice_with_notice_reference.pem`` - An RSA 2048 bit self-signed
   certificate containing a certificate policies extension with a
   notice reference in the user notice.
diff --git a/vectors/cryptography_vectors/x509/custom/nc_invalid_ip_netmask.pem b/vectors/cryptography_vectors/x509/custom/nc_invalid_ip_netmask.pem
new file mode 100644
index 0000000..42f7fd3
--- /dev/null
+++ b/vectors/cryptography_vectors/x509/custom/nc_invalid_ip_netmask.pem
@@ -0,0 +1,18 @@
+-----BEGIN CERTIFICATE-----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+-----END CERTIFICATE-----