diff --git a/rai/node/bootstrap.cpp b/rai/node/bootstrap.cpp
index 79286531..adc42117 100644
--- a/rai/node/bootstrap.cpp
+++ b/rai/node/bootstrap.cpp
@@ -813,8 +813,15 @@ void rai::bootstrap_initiator::initiate (rai::endpoint const & endpoint_a)
     processor->run (rai::tcp_endpoint (endpoint_a.address (), endpoint_a.port ()));
 }
 
+void rai::bootstrap_initiator::add_observer (std::function <void (bool)> const & observer_a)
+{
+	std::lock_guard <std::mutex> lock (mutex);
+	observers.push_back (observer_a);
+}
+
 void rai::bootstrap_initiator::notify_listeners ()
 {
+	assert (!mutex.try_lock());
 	for (auto & i: observers)
 	{
 		i (in_progress);
diff --git a/rai/node/bootstrap.hpp b/rai/node/bootstrap.hpp
index 675509b2..628e3c7c 100644
--- a/rai/node/bootstrap.hpp
+++ b/rai/node/bootstrap.hpp
@@ -106,7 +106,6 @@ public:
     std::shared_ptr <rai::frontier_req_client> connection;
     rai::push_synchronization synchronization;
 };
-
 class bootstrap_initiator
 {
 public:
@@ -116,11 +115,13 @@ public:
     void bootstrap_any ();
 	void initiate (rai::endpoint const &);
 	void notify_listeners ();
-	std::vector <std::function <void (bool)>> observers;
+	void add_observer (std::function <void (bool)> const &);
 	std::mutex mutex;
 	rai::node & node;
 	bool in_progress;
 	std::unordered_set <rai::endpoint> warmed_up;
+private:
+	std::vector <std::function <void (bool)>> observers;
 };
 class bootstrap_listener
 {
diff --git a/rai/qt/qt.cpp b/rai/qt/qt.cpp
index 3b98a6f4..6dfe54b5 100644
--- a/rai/qt/qt.cpp
+++ b/rai/qt/qt.cpp
@@ -764,7 +764,7 @@ active_status (*this)
 			update_connected ();
 		}));
 	});
-	node.bootstrap_initiator.observers.push_back ([this] (bool active_a)
+	node.bootstrap_initiator.add_observer ([this] (bool active_a)
 	{
 		application.postEvent (&processor, new eventloop_event ([this, active_a] ()
 		{