diff --git a/slixmpp/features/feature_starttls/stanza.py b/slixmpp/features/feature_starttls/stanza.py
index 70979402..f433f1b2 100644
--- a/slixmpp/features/feature_starttls/stanza.py
+++ b/slixmpp/features/feature_starttls/stanza.py
@@ -3,8 +3,12 @@
 # Copyright (C) 2011  Nathanael C. Fritz
 # This file is part of Slixmpp.
 # See the file LICENSE for copying permission.
-from slixmpp.xmlstream import StanzaBase, ElementBase
 from typing import Set, ClassVar
+from slixmpp.xmlstream import StanzaBase, ElementBase
+from slixmpp.xmlstream.xmlstream import InvalidCABundle
+
+import logging
+log = logging.getLogger(__name__)
 
 
 class STARTTLS(StanzaBase):
@@ -36,6 +40,12 @@ class Proceed(StanzaBase):
     namespace = 'urn:ietf:params:xml:ns:xmpp-tls'
     interfaces: ClassVar[Set[str]] = set()
 
+    def exception(self, e: Exception) -> None:
+        log.exception('Error handling {%s}%s stanza',
+                      self.namespace, self.name)
+        if isinstance(e, InvalidCABundle):
+            raise e
+
 
 class Failure(StanzaBase):
     """