diff --git a/lldb/source/Core/Communication.cpp b/lldb/source/Core/Communication.cpp
index a43ed2e929d6..a9ca35c9db85 100644
--- a/lldb/source/Core/Communication.cpp
+++ b/lldb/source/Core/Communication.cpp
@@ -64,6 +64,7 @@ Communication::~Communication()
 void
 Communication::Clear()
 {
+    SetReadThreadBytesReceivedCallback (NULL, NULL);
     StopReadThread (NULL);
     Disconnect (NULL);
 }
@@ -295,7 +296,7 @@ Communication::AppendBytesToCache (const uint8_t * bytes, size_t len, bool broad
         // If the user registered a callback, then call it and do not broadcast
         m_callback (m_callback_baton, bytes, len);
     }
-    else
+    else if (bytes != NULL && len > 0)
     {
         Mutex::Locker locker(m_bytes_mutex);
         m_bytes.append ((const char *)bytes, len);