diff --git a/src/com/fsck/k9/activity/MessageList.java b/src/com/fsck/k9/activity/MessageList.java
index 97391093f..262110a77 100644
--- a/src/com/fsck/k9/activity/MessageList.java
+++ b/src/com/fsck/k9/activity/MessageList.java
@@ -2058,8 +2058,16 @@ public class MessageList
             addOrUpdateMessages(account, folder, messages, verifyAgainstSearch);
         }
 
-        private void addOrUpdateMessages(Account account, String folder, List<Message> messages, boolean verifyAgainstSearch)
+        private void addOrUpdateMessages(final Account account, final String folder, final List<Message> providedMessages, final boolean verifyAgainstSearch)
         {
+            // we copy the message list because the callback doesn't expect
+            // the callbacks to mutate it. 
+            final List<Message> messages = new ArrayList<Message>(providedMessages);
+
+            runOnUiThread(new Runnable()
+            {
+                public void run()
+                {
                     boolean needsSort = false;
                     final List<MessageInfoHolder> messagesToAdd = new ArrayList<MessageInfoHolder>();
                     List<MessageInfoHolder> messagesToRemove = new ArrayList<MessageInfoHolder>();
@@ -2133,6 +2141,8 @@ public class MessageList
                         mHandler.sortMessages();
                         mHandler.resetUnreadCount();
                     }
+                }
+            });
         }
         public MessageInfoHolder getMessage(Message message)
         {