Index: src/view/kateview.cpp
===================================================================
--- src/view/kateview.cpp
+++ src/view/kateview.cpp
@@ -547,8 +547,9 @@
         a = m_toggleWriteLock = new KToggleAction(i18n("&Read Only Mode"), this);
         a->setWhatsThis(i18n("Lock/unlock the document for writing"));
         a->setChecked(!doc()->isReadWrite());
-        connect(a, SIGNAL(triggered(bool)), SLOT(toggleWriteLock()));
         ac->addAction(QStringLiteral("tools_toggle_write_lock"), a);
+        connect(a, SIGNAL(triggered(bool)), SLOT(toggleWriteLock()));
+        connect(document(), &KTextEditor::DocumentPrivate::modifiedChanged, [=] { m_toggleWriteLock->setEnabled(!doc()->isModified()); });
 
         a = ac->addAction(QStringLiteral("tools_uppercase"));
         a->setIcon(QIcon::fromTheme(QStringLiteral("format-text-uppercase")));