diff --git a/src/librf625.cpp b/src/librf625.cpp
index 8969ba8181df3dee7e266a8959f4cf2b40b6754b..776479681195511e8181288d2da6d4a7b91966c3 100644
--- a/src/librf625.cpp
+++ b/src/librf625.cpp
@@ -862,14 +862,16 @@ void rf625::udp_register_callback(rf625_udp_proc proc)
 
 void rf625::udp_unregister_callback()
 {
+    m_callback_mx.lock();
+
     if (m_callback) {
-        m_callback_mx.lock();
         m_callback = nullptr;
         m_thread->join();
         delete m_thread;
         m_thread = nullptr;
-        m_callback_mx.unlock();
     }
+
+    m_callback_mx.unlock();
 }
 
 /*! Main routine for processing broadcast commands