diff --git a/autotests/integration/CMakeLists.txt b/autotests/integration/CMakeLists.txt
index 75d88c9317..cd86c04971 100644
--- a/autotests/integration/CMakeLists.txt
+++ b/autotests/integration/CMakeLists.txt
@@ -52,6 +52,7 @@ if (XCB_ICCCM_FOUND)
     integrationTest(NAME testX11DesktopWindow SRCS desktop_window_x11_test.cpp LIBS XCB::ICCCM)
     integrationTest(NAME testXwaylandInput SRCS xwayland_input_test.cpp LIBS XCB::ICCCM)
     integrationTest(NAME testWindowRules SRCS window_rules_test.cpp LIBS XCB::ICCCM)
+    integrationTest(NAME testX11Client SRCS x11_client_test.cpp LIBS XCB::ICCCM)
 
     if (KWIN_BUILD_ACTIVITIES)
         integrationTest(NAME testActivities SRCS activities_test.cpp LIBS XCB::ICCCM)
diff --git a/autotests/integration/shell_client_test.cpp b/autotests/integration/shell_client_test.cpp
index 4453cfdfac..c6740d2ace 100644
--- a/autotests/integration/shell_client_test.cpp
+++ b/autotests/integration/shell_client_test.cpp
@@ -60,6 +60,7 @@ private Q_SLOTS:
     void testMaximizedToFullscreen();
     void testWindowOpensLargerThanScreen_data();
     void testWindowOpensLargerThanScreen();
+    void testCaptionSimplified();
 };
 
 void TestShellClient::initTestCase()
@@ -544,5 +545,22 @@ void TestShellClient::testWindowOpensLargerThanScreen()
     QVERIFY(sizeChangeRequestedSpy.wait());
 }
 
+void TestShellClient::testCaptionSimplified()
+{
+    // this test verifies that caption is properly trimmed
+    // see BUG 323798 comment #12
+    QScopedPointer<Surface> surface(Test::createSurface());
+    // only done for xdg-shell as ShellSurface misses the setter
+    QScopedPointer<XdgShellSurface> shellSurface(qobject_cast<XdgShellSurface*>(Test::createShellSurface(Test::ShellSurfaceType::XdgShellV5, surface.data())));
+    const QString origTitle = QString::fromUtf8(QByteArrayLiteral("Was tun, wenn Schüler Autismus haben?\342\200\250\342\200\250\342\200\250 – Marlies Hübner - Mozilla Firefox"));
+    shellSurface->setTitle(origTitle);
+    auto c = Test::renderAndWaitForShown(surface.data(), QSize(100, 50), Qt::blue);
+    QVERIFY(c);
+    QEXPECT_FAIL("", "BUG 323798", Continue);
+    QVERIFY(c->caption() != origTitle);
+    QEXPECT_FAIL("", "BUG 323798", Continue);
+    QCOMPARE(c->caption(), origTitle.simplified());
+}
+
 WAYLANDTEST_MAIN(TestShellClient)
 #include "shell_client_test.moc"
diff --git a/autotests/integration/x11_client_test.cpp b/autotests/integration/x11_client_test.cpp
new file mode 100644
index 0000000000..0ca060ca7e
--- /dev/null
+++ b/autotests/integration/x11_client_test.cpp
@@ -0,0 +1,131 @@
+/********************************************************************
+KWin - the KDE window manager
+This file is part of the KDE project.
+
+Copyright (C) 2016 Martin Gräßlin <mgraesslin@kde.org>
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*********************************************************************/
+#include "kwin_wayland_test.h"
+#include "composite.h"
+#include "effects.h"
+#include "effectloader.h"
+#include "cursor.h"
+#include "platform.h"
+#include "scene_qpainter.h"
+#include "shell_client.h"
+#include "wayland_server.h"
+#include "workspace.h"
+
+#include <netwm.h>
+#include <xcb/xcb_icccm.h>
+
+using namespace KWin;
+static const QString s_socketName = QStringLiteral("wayland_test_x11_client-0");
+
+class X11ClientTest : public QObject
+{
+Q_OBJECT
+private Q_SLOTS:
+    void initTestCase();
+    void init();
+    void cleanup();
+
+    void testCaptionSimplified();
+};
+
+void X11ClientTest::initTestCase()
+{
+    qRegisterMetaType<KWin::AbstractClient*>();
+    QSignalSpy workspaceCreatedSpy(kwinApp(), &Application::workspaceCreated);
+    QVERIFY(workspaceCreatedSpy.isValid());
+    kwinApp()->platform()->setInitialWindowSize(QSize(1280, 1024));
+    QVERIFY(waylandServer()->init(s_socketName.toLocal8Bit()));
+
+    kwinApp()->start();
+    QVERIFY(workspaceCreatedSpy.wait());
+    QVERIFY(Compositor::self());
+}
+
+void X11ClientTest::init()
+{
+}
+
+void X11ClientTest::cleanup()
+{
+}
+
+struct XcbConnectionDeleter
+{
+    static inline void cleanup(xcb_connection_t *pointer)
+    {
+        xcb_disconnect(pointer);
+    }
+};
+
+
+void X11ClientTest::testCaptionSimplified()
+{
+    // this test verifies that caption is properly trimmed
+    // see BUG 323798 comment #12
+    QSignalSpy windowAddedSpy(effects, &EffectsHandler::windowAdded);
+    QVERIFY(windowAddedSpy.isValid());
+
+    // create an xcb window
+    QScopedPointer<xcb_connection_t, XcbConnectionDeleter> c(xcb_connect(nullptr, nullptr));
+    QVERIFY(!xcb_connection_has_error(c.data()));
+    const QRect windowGeometry(0, 0, 100, 200);
+    xcb_window_t w = xcb_generate_id(c.data());
+    xcb_create_window(c.data(), XCB_COPY_FROM_PARENT, w, rootWindow(),
+                      windowGeometry.x(),
+                      windowGeometry.y(),
+                      windowGeometry.width(),
+                      windowGeometry.height(),
+                      0, XCB_WINDOW_CLASS_INPUT_OUTPUT, XCB_COPY_FROM_PARENT, 0, nullptr);
+    xcb_size_hints_t hints;
+    memset(&hints, 0, sizeof(hints));
+    xcb_icccm_size_hints_set_position(&hints, 1, windowGeometry.x(), windowGeometry.y());
+    xcb_icccm_size_hints_set_size(&hints, 1, windowGeometry.width(), windowGeometry.height());
+    xcb_icccm_set_wm_normal_hints(c.data(), w, &hints);
+    NETWinInfo winInfo(c.data(), w, rootWindow(), NET::Properties(), NET::Properties2());
+    const QByteArray origTitle = QByteArrayLiteral("Was tun, wenn Schüler Autismus haben?\342\200\250\342\200\250\342\200\250 – Marlies Hübner - Mozilla Firefox");
+    winInfo.setName(origTitle.constData());
+    xcb_map_window(c.data(), w);
+    xcb_flush(c.data());
+
+    // we should get a client for it
+    QSignalSpy windowCreatedSpy(workspace(), &Workspace::clientAdded);
+    QVERIFY(windowCreatedSpy.isValid());
+    QVERIFY(windowCreatedSpy.wait());
+    Client *client = windowCreatedSpy.first().first().value<Client*>();
+    QVERIFY(client);
+    QCOMPARE(client->window(), w);
+    QEXPECT_FAIL("", "BUG 323798", Continue);
+    QVERIFY(client->caption() != QString::fromUtf8(origTitle));
+    QEXPECT_FAIL("", "BUG 323798", Continue);
+    QCOMPARE(client->caption(), QString::fromUtf8(origTitle).simplified());
+
+    // and destroy the window again
+    xcb_unmap_window(c.data(), w);
+    xcb_flush(c.data());
+
+    QSignalSpy windowClosedSpy(client, &Client::windowClosed);
+    QVERIFY(windowClosedSpy.isValid());
+    QVERIFY(windowClosedSpy.wait());
+    xcb_destroy_window(c.data(), w);
+    c.reset();
+}
+
+WAYLANDTEST_MAIN(X11ClientTest)
+#include "x11_client_test.moc"