diff --git a/isso/comment.py b/isso/comment.py
index 35ae838..6754140 100644
--- a/isso/comment.py
+++ b/isso/comment.py
@@ -36,10 +36,12 @@ def create(app, environ, request, path):
     except ValueError:
         return abort(400)
 
+    md5 = rv.md5
     rv.text = app.markup.convert(rv.text)
+
     response = Response(json.dumps(rv), 201, content_type='application/json')
     response.set_cookie('session-%s-%s' % (urllib.quote(path, ''), rv.id),
-        app.signer.dumps([path, rv.id]), max_age=app.MAX_AGE)
+        app.signer.dumps([path, rv.id, md5]), max_age=app.MAX_AGE)
     return response
 
 
@@ -65,14 +67,23 @@ def modify(app, environ, request, path, id):
     except (SignatureExpired, BadSignature):
         return abort(403)
 
-    if not (rv[0] == '*' or rv == [path, id]):
+    # verify checksum, mallory might skip cookie deletion when he deletes a comment
+    if app.db.get(path, id).md5 != rv[2]:
+        abort(403)
+
+    if not (rv[0] == '*' or rv[0:2] == [path, id]):
         abort(401)
 
     if request.method == 'PUT':
         try:
             rv = app.db.update(path, id, models.Comment.fromjson(request.data))
+            return Response(json.dumps(rv), 200, content_type='application/json')
         except ValueError as e:
             return Response(unicode(e), 400)
-    else:
+
+    if request.method == 'DELETE':
         rv = app.db.delete(path, id)
-    return Response(json.dumps(rv), 200, content_type='application/json')
+
+        response = Response(json.dumps(rv), 200, content_type='application/json')
+        response.delete_cookie('session-%s-%s' % (urllib.quote(path, ''), id))
+        return response
diff --git a/isso/models.py b/isso/models.py
index dfffd3e..e8d10a4 100644
--- a/isso/models.py
+++ b/isso/models.py
@@ -5,6 +5,7 @@
 
 import json
 import time
+import hashlib
 
 class Comment(object):
     """This class represents a regular comment. It needs at least a text
@@ -56,3 +57,10 @@ class Comment(object):
     @property
     def deleted(self):
         return self.mode == 4
+
+    @property
+    def md5(self):
+        hv = hashlib.md5()
+        for key in set(self.fields) - set(['parent', ]):
+            hv.update(getattr(self, key) or '')
+        return hv.hexdigest()
diff --git a/specs/test_comment.py b/specs/test_comment.py
index 42aca49..0513d3a 100644
--- a/specs/test_comment.py
+++ b/specs/test_comment.py
@@ -115,3 +115,15 @@ class TestComments(unittest.TestCase):
         for path in paths:
             assert self.get('/comment/' + path)
             assert self.get('/comment/' + path + '/1')
+
+    def testDeleteAndCreateByDifferentUsersButSamePostId(self):
+
+        mallory = Client(self.app, Response)
+        mallory.post('/comment/path/new', data=json.dumps(comment(text='Foo')))
+        mallory.delete('/comment/path/1')
+
+        bob = Client(self.app, Response)
+        bob.post('/comment/path/new', data=json.dumps(comment(text='Bar')))
+
+        assert mallory.delete('/comment/path/1').status_code == 403
+        assert bob.delete('/comment/path/1').status_code == 200