diff --git a/src/xdgactivationv1.cpp b/src/xdgactivationv1.cpp
index e15fa201ce..9048e25f2a 100644
--- a/src/xdgactivationv1.cpp
+++ b/src/xdgactivationv1.cpp
@@ -17,6 +17,7 @@
 #include "wayland_server.h"
 #include "window.h"
 #include "workspace.h"
+#include <KApplicationTrader>
 #include <KDesktopFile>
 
 using namespace KWaylandServer;
@@ -31,6 +32,25 @@ static bool isPrivilegedInWindowManagement(const ClientConnection *client)
     return requestedInterfaces.contains(QLatin1String("org_kde_plasma_window_management"));
 }
 
+static const QString windowDesktopFileName(Window *window)
+{
+    QString ret = window->desktopFileName();
+    if (!ret.isEmpty()) {
+        return ret;
+    }
+
+    // Fallback to StartupWMClass for legacy apps
+    const auto resourceName = window->resourceName();
+    const auto service = KApplicationTrader::query([&resourceName](const KService::Ptr &service) {
+        return service->property("StartupWMClass") == resourceName;
+    });
+
+    if (!service.isEmpty()) {
+        ret = service.constFirst()->desktopEntryName();
+    }
+    return ret;
+}
+
 XdgActivationV1Integration::XdgActivationV1Integration(XdgActivationV1Interface *activation, QObject *parent)
     : QObject(parent)
 {
@@ -41,7 +61,7 @@ XdgActivationV1Integration::XdgActivationV1Integration(XdgActivationV1Interface
         }
 
         // We check that it's not the app that we are trying to activate
-        if (window->desktopFileName() != m_currentActivationToken->applicationId) {
+        if (windowDesktopFileName(window) != m_currentActivationToken->applicationId) {
             // But also that the new one has been requested after the token was requested
             if (window->lastUsageSerial() < m_currentActivationToken->serial) {
                 return;