diff --git a/lib/models.py b/lib/models.py
index 239f404..d968677 100644
--- a/lib/models.py
+++ b/lib/models.py
@@ -135,14 +135,26 @@ class Subject(db.Model):
     return None
 
   @db.transactional()
-  def SendMessage(self, message, sender, key=None):
+  def PutMessage(self, message, sender, key=None):
+    """Internal helper for SendMessage().
+
+    Unless/until channel.send_message becomes transactional, we have to finish
+    the datastore work (and any retries) before we start transmitting to
+    channels.
+    """
     obj = Message(parent=self, message=message, sender=sender, key_=key)
     obj.put()
 
-    event = obj.ToEvent()
+    return (
+        obj,
+        [Subscription.client.get_value_for_datastore(subscription)
+         for subscription in Subscription.all().ancestor(self)])
 
-    for subscription in Subscription.all().ancestor(self):
-      Client.SendByKey(Subscription.client.get_value_for_datastore(subscription), event)
+  def SendMessage(self, message, sender, key=None):
+    obj, subscriptions = self.PutMessage(message, sender, key)
+    event = obj.ToEvent()
+    for subscription in subscriptions:
+      Client.SendByKey(subscription, event)
 
 
 class Subscription(db.Model):
diff --git a/static/cosmopolite.js b/static/cosmopolite.js
index 688cf95..99c41de 100644
--- a/static/cosmopolite.js
+++ b/static/cosmopolite.js
@@ -448,7 +448,9 @@ Cosmopolite.prototype.onServerEvent_ = function(e) {
  */
 Cosmopolite.prototype.onSocketError_ = function(msg) {
   console.log('cosmopolite: socket error:', msg);
-  this.socket_.close();
+  if (this.socket_) {
+    this.socket_.close();
+  }
 };
 
 /* Exported values */
diff --git a/static/test.html b/static/test.html
index 22fe1d0..7242235 100644
--- a/static/test.html
+++ b/static/test.html
@@ -77,6 +77,56 @@ asyncTest('Message round trip', function() {
   var cosmo2 = new Cosmopolite(callbacks2, null, randstring());
 });
 
+asyncTest('Overwrite key', function() {
+  expect(8);
+
+  var subject = randstring();
+  var message1 = randstring();
+  var message2 = randstring();
+  var key = randstring();
+
+  var messages1 = 0;
+
+  var callbacks1 = {
+    'onReady': function() {
+      cosmo1.subscribe(subject, -1);
+      cosmo1.sendMessage(subject, message1, key);
+    },
+    'onMessage': function(e) {
+      messages1++;
+      if (messages1 == 1) {
+        cosmo1.sendMessage(subject, message2, key);
+      }
+    },
+  };
+
+  var messages2 = 0;
+
+  var callbacks2 = {
+    'onReady': function() {
+      cosmo2.subscribe(subject, -1);
+    },
+    'onMessage': function(e) {
+      messages2++;
+      equal(e['subject'], subject, 'subject matches');
+      equal(e['key'], key, 'key matches');
+      if (messages2 == 1) {
+        equal(e['message'], message1, 'message #1 matches');
+        equal(cosmo2.getKeyMessage(subject, key)['message'], message1, 'message #1 matches by key')
+        return;
+      }
+      equal(e['message'], message2, 'message #2 matches');
+      equal(cosmo2.getKeyMessage(subject, key)['message'], message2, 'message #2 matches by key')
+      cosmo1.shutdown();
+      cosmo2.shutdown();
+      start();
+    },
+  };
+
+  var cosmo1 = new Cosmopolite(callbacks1, null, randstring());
+  var cosmo2 = new Cosmopolite(callbacks2, null, randstring());
+});
+
   </script>
 </body>
 </html>