Index: src/progressdialog.cpp
===================================================================
--- src/progressdialog.cpp (revision 5f1602ef2512b6a907744ba59be88e0390453929)
+++ src/progressdialog.cpp (revision 938fda69b191f4bb6f9744fad17371e01dd772a9)
@@ -36,8 +36,11 @@
 	// TODO: sigc::bind to on_thread_entry
 	m_entry_func = entry_func;
+
+	lock();
 	m_thread = Glib::Thread::create(
 		sigc::mem_fun(*this, &Thread::on_thread_entry),
 		false
 	);
+	unlock();
 }
 
@@ -88,4 +91,7 @@
 	try
 	{
+		lock();
+		unlock();
+
 		// Call working function
 		m_entry_func(*this);