diff --git a/sources/qetapp.cpp b/sources/qetapp.cpp
index 3de743760..9afb2e300 100644
--- a/sources/qetapp.cpp
+++ b/sources/qetapp.cpp
@@ -1659,7 +1659,31 @@ void QETApp::receiveMessage(int instanceId, QByteArray message)
 	{
 		QString my_message(str.mid(20));
 		QStringList args_list = QET::splitWithSpaces(my_message);
-		openFiles(QETArguments(args_list));
+
+			// Deferred, not called directly.
+			//
+			// This slot runs inside SingleApplication's readyRead handling:
+			// SingleApplicationPrivate::slotDataAvailable() emits
+			// receivedMessage() synchronously from the socket's readyRead
+			// lambda. openFiles() then loads a project -- seconds of work on
+			// a large one -- and openAndAddProject() puts up a modal
+			// BackupDialog, whose exec() runs a nested event loop while the
+			// socket handler is still on the stack.
+			//
+			// During that nested loop the secondary instance exits, the
+			// connection closes and the QLocalSocket is deleted. When the
+			// dialog is dismissed and the stack unwinds, QMetaObject::
+			// activate() continues emitting on the freed sender and the
+			// process dies. Reported with a backtrace on PR #861;
+			// reproduced on Qt 6.10.2 by dismissing the dialog, which is the
+			// step that makes it fail -- leaving it open never unwinds.
+			//
+			// A zero-timer returns to the event loop first, so the socket
+			// stack is fully unwound before any of this runs.
+		const QETArguments deferred_args{args_list};
+		QTimer::singleShot(0, this, [this, deferred_args]() {
+			openFiles(deferred_args);
+		});
 	}
 }