diff --git a/CHANGES.txt b/CHANGES.txt
index 81c7da2..7329c5d 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -4,6 +4,10 @@ Changelog
 2.0b2 (Unreleased)
 ------------------
 
+- Fix unindexing of comments when deleting content resulting from
+  iterating over a BTree while modifying it. Fixes #11402.
+  [rossp]
+
 - Fix Missing.Value for Creator in the catalog. Fixes #11634.
   [rossp]
 
diff --git a/plone/app/discussion/comment.py b/plone/app/discussion/comment.py
index 98d8d39..e924b60 100644
--- a/plone/app/discussion/comment.py
+++ b/plone/app/discussion/comment.py
@@ -195,14 +195,16 @@ def notify_content_object(obj, event):
                                     'last_comment_date',
                                     'commentators',))
 
+
 def notify_content_object_deleted(obj, event):
     """Remove all comments of a content object when the content object has been
        deleted.
     """
     if IAnnotatable.providedBy(obj):
         conversation = IConversation(obj)
-        for comment in conversation.getComments():
-            del conversation[comment.id]
+        while conversation:
+            del conversation[conversation.keys()[0]]
+
 
 def notify_user(obj, event):
     """Tell users when a comment has been added.
diff --git a/plone/app/discussion/tests/functional_test_comments.txt b/plone/app/discussion/tests/functional_test_comments.txt
index ff96f0d..33f675e 100644
--- a/plone/app/discussion/tests/functional_test_comments.txt
+++ b/plone/app/discussion/tests/functional_test_comments.txt
@@ -35,7 +35,8 @@ Make sure we have a test user from the layer and it uses fancy characters:
 
     >>> from Products.CMFCore.utils import getToolByName
     >>> mtool = getToolByName(portal, 'portal_membership', None)
-    >>> mtool.getMemberById('jim').getProperty('fullname')
+    >>> jim_fullname = mtool.getMemberById('jim').getProperty('fullname')
+    >>> jim_fullname
     'Jim Fult\xc3\xb8rn'
 
 Enable commenting.
@@ -198,11 +199,12 @@ Now we can post an anonymous comment.
 Make sure special characters work as well.
 
     >>> unprivileged_browser.open(urldoc1)
-    >>> unprivileged_browser.getControl(name='form.widgets.author_name').value = "Tarek Ziadé"
+    >>> tarek_fullname = "Tarek Ziadé"
+    >>> unprivileged_browser.getControl(name='form.widgets.author_name').value = tarek_fullname
     >>> unprivileged_browser.getControl(name='form.widgets.text').value = "This is an äüö comment"
     >>> unprivileged_browser.getControl(name='form.buttons.comment').click()
 
-    >>> 'Tarek Ziadé' in unprivileged_browser.contents
+    >>> tarek_fullname in unprivileged_browser.contents
     True
     
     >>> 'says' in unprivileged_browser.contents
@@ -313,6 +315,7 @@ Create a collection.
     >>> browser.getControl('Save').click()
     >>> print browser.contents
     <...Changes saved...
+    >>> topic_url = browser.url
 
 Set the collection criteria.
 
@@ -339,7 +342,40 @@ View the collection listing.
     <Link text='Anonymous on Doc1' url='http://nohost/plone/doc1/++conversation++default/...'>
     >>> browser.getLink('Anonymous on Doc1', index=1)
     <Link text='Anonymous on Doc1' url='http://nohost/plone/doc1/++conversation++default/...'>
-    >>> browser.getLink('Tarek Ziadé on Doc1')
+    >>> browser.getLink(tarek_fullname + ' on Doc1')
     <Link text='Tarek Ziad\xc3\xa9 on Doc1' url='http://nohost/plone/doc1/++conversation++default/...'>
-    >>> browser.getLink('Jim Fultørn on Doc1')
+    >>> browser.getLink(jim_fullname + ' on Doc1')
     <Link text='Jim Fult\xc3\xb8rn on Doc1' url='http://nohost/plone/doc1/++conversation++default/...'>
+
+Comments are unindexed when the content is deleted
+--------------------------------------------------
+
+Delete the commented content.
+
+    >>> browser.open(urldoc1)
+    >>> browser.getLink('Delete').click()
+    >>> browser.getControl('Delete').click()
+    >>> print browser.contents
+    <...Doc1 has been deleted...
+
+The comments are no longer in the catalog.
+
+    >>> browser.open(topic_url)
+    >>> browser.getLink('admin on Doc1', index=0)
+    Traceback (most recent call last):
+    LinkNotFoundError
+    >>> browser.getLink('admin on Doc1', index=1)
+    Traceback (most recent call last):
+    LinkNotFoundError
+    >>> browser.getLink('Anonymous on Doc1', index=0)
+    Traceback (most recent call last):
+    LinkNotFoundError
+    >>> browser.getLink('Anonymous on Doc1', index=1)
+    Traceback (most recent call last):
+    LinkNotFoundError
+    >>> browser.getLink(tarek_fullname + ' on Doc1')
+    Traceback (most recent call last):
+    LinkNotFoundError
+    >>> browser.getLink(jim_fullname + ' on Doc1')
+    Traceback (most recent call last):
+    LinkNotFoundError