diff --git a/sources/machine_info.h b/sources/machine_info.h
index 04f074f6d..58866184b 100644
--- a/sources/machine_info.h
+++ b/sources/machine_info.h
@@ -75,11 +75,11 @@ class MachineInfo
 	{
 		struct Screen
 		{
-			int32_t count;
-			int32_t width[10];
-			int32_t height[10];
-			int32_t Max_width;
-			int32_t Max_height;
+			int32_t count     = 0;
+			int32_t width[10] = {};
+			int32_t height[10]= {};
+			int32_t Max_width = 0;
+			int32_t Max_height= 0;
 		}screen;
 		struct Built
 		{
diff --git a/sources/main.cpp b/sources/main.cpp
index 8f54279b5..ee70a90ac 100644
--- a/sources/main.cpp
+++ b/sources/main.cpp
@@ -241,6 +241,11 @@ QGuiApplication::setHighDpiScaleFactorRoundingPolicy(QetSettings::hdpiScaleFacto
 	QObject::connect(&app, &SingleApplication::receivedMessage,
 			 &qetapp, &QETApp::receiveMessage);
 
+	// Pre-initialise on the main (GUI) thread: the constructor calls
+	// qApp->screens() which is not thread-safe in Qt5 — calling instance()
+	// here guarantees the singleton is fully built before the worker runs.
+	MachineInfo::instance();
+
 	QtConcurrent::run([=]()
 	{
 		// for debugging
diff --git a/sources/qetdiagrameditor.h b/sources/qetdiagrameditor.h
index d5139ed5a..5a26b5f06 100644
--- a/sources/qetdiagrameditor.h
+++ b/sources/qetdiagrameditor.h
@@ -80,6 +80,11 @@ class QETDiagramEditor : public QETMainWindow
 	  protected:
 		bool event(QEvent *) override;
 	private:
+		// Declared first so it is initialised before any member whose
+		// constructor may dispatch a Qt event calling event() (e.g. the
+		// QActionGroup members below trigger QObject::setParent events).
+		bool m_first_show = true;
+
 		QETDiagramEditor(const QETDiagramEditor &);
 		void setUpElementsPanel ();
 		void setUpElementsCollectionWidget();
@@ -253,7 +258,6 @@ class QETDiagramEditor : public QETMainWindow
 		QUndoGroup undo_group;
 		AutoNumberingDockWidget *m_autonumbering_dock;
 		int activeSubWindowIndex;
-		bool m_first_show = true;
 		SearchAndReplaceWidget m_search_and_replace_widget;
 };
 #endif