update exception to contain detail
diff --git a/docs/x509.rst b/docs/x509.rst
index 0ce9016..2e4a0ef 100644
--- a/docs/x509.rst
+++ b/docs/x509.rst
@@ -274,6 +274,9 @@
         :raises cryptography.x509.UnsupportedExtension: If the certificate
             contains an extension that is not supported.
 
+        :raises cryptography.x509.UnsupportedGeneralNameType: If an extension
+            contains a general name that is not supported.
+
         .. doctest::
 
             >>> for ext in cert.extensions:
@@ -969,6 +972,10 @@
     This is raised when a certificate contains an unsupported general name
     type in an extension.
 
+    .. attribute:: type
+
+        :type: :term:`text` or int
+
 
 .. _`public key infrastructure`: https://en.wikipedia.org/wiki/Public_key_infrastructure
 .. _`TLS`: https://en.wikipedia.org/wiki/Transport_Layer_Security
diff --git a/src/cryptography/hazmat/backends/openssl/x509.py b/src/cryptography/hazmat/backends/openssl/x509.py
index affb79d..07e79fe 100644
--- a/src/cryptography/hazmat/backends/openssl/x509.py
+++ b/src/cryptography/hazmat/backends/openssl/x509.py
@@ -68,7 +68,8 @@
         raise x509.UnsupportedGeneralNameType(
             "{0} is not a supported type".format(
                 x509._GENERAL_NAMES.get(gn.type, gn.type)
-            )
+            ),
+            x509._GENERAL_NAMES.get(gn.type, gn.type)
         )
 
 
diff --git a/src/cryptography/x509.py b/src/cryptography/x509.py
index 3dc066f..dd6ea92 100644
--- a/src/cryptography/x509.py
+++ b/src/cryptography/x509.py
@@ -129,7 +129,9 @@
 
 
 class UnsupportedGeneralNameType(Exception):
-    pass
+    def __init__(self, msg, type):
+        super(UnsupportedGeneralNameType, self).__init__(msg)
+        self.type = type
 
 
 class NameAttribute(object):
diff --git a/tests/test_x509_ext.py b/tests/test_x509_ext.py
index 5f175c4..c17beba 100644
--- a/tests/test_x509_ext.py
+++ b/tests/test_x509_ext.py
@@ -766,5 +766,7 @@
             x509.load_pem_x509_certificate,
             backend
         )
-        with pytest.raises(x509.UnsupportedGeneralNameType):
+        with pytest.raises(x509.UnsupportedGeneralNameType) as exc:
             cert.extensions
+
+        assert exc.value.type == "otherName"