diff --git a/sleekxmpp/stanza/error.py b/sleekxmpp/stanza/error.py
index 1f4b3d8..ee46722 100644
--- a/sleekxmpp/stanza/error.py
+++ b/sleekxmpp/stanza/error.py
@@ -11,7 +11,7 @@ class Error(ElementBase):
 	namespace = 'jabber:client'
 	name = 'error'
 	plugin_attrib = 'error'
-	conditions = set(('bad-request', 'conflict', 'feature-not-implemented', 'forbidden', 'gone', 'item-not-found', 'jid-malformed', 'not-acceptable', 'not-allowed', 'not-authorized', 'payment-required', 'recipient-unavailable', 'redirect', 'registration-required', 'remote-server-not-found', 'remote-server-timeout', 'resource-constraint', 'service-unavailable', 'subscription-required', 'undefined-condition', 'unexpected-request'))
+	conditions = set(('bad-request', 'conflict', 'feature-not-implemented', 'forbidden', 'gone', 'internal-server-error', 'item-not-found', 'jid-malformed', 'not-acceptable', 'not-allowed', 'not-authorized', 'payment-required', 'recipient-unavailable', 'redirect', 'registration-required', 'remote-server-not-found', 'remote-server-timeout', 'resource-constraint', 'service-unavailable', 'subscription-required', 'undefined-condition', 'unexpected-request'))
 	interfaces = set(('code', 'condition', 'text', 'type'))
 	types = set(('cancel', 'continue', 'modify', 'auth', 'wait'))
 	sub_interfaces = set(('text',))