diff --git a/autotests/CMakeLists.txt b/autotests/CMakeLists.txt
--- a/autotests/CMakeLists.txt
+++ b/autotests/CMakeLists.txt
@@ -310,3 +310,14 @@
 
 add_test(kwin_testScreenEdges testScreenEdges)
 ecm_mark_as_test(testScreenEdges)
+
+########################################################
+# Test X11 TimestampUpdate
+########################################################
+add_executable(testX11TimestampUpdate test_x11_timestamp_update.cpp)
+target_link_libraries(testX11TimestampUpdate
+    Qt5::Test
+    kwin
+)
+add_test(kwin-testX11TimestampUpdate testX11TimestampUpdate)
+ecm_mark_as_test(testX11TimestampUpdate)
diff --git a/autotests/test_x11_timestamp_update.cpp b/autotests/test_x11_timestamp_update.cpp
new file mode 100644
--- /dev/null
+++ b/autotests/test_x11_timestamp_update.cpp
@@ -0,0 +1,123 @@
+/********************************************************************
+KWin - the KDE window manager
+This file is part of the KDE project.
+
+Copyright (C) 2017 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 <QTest>
+#include <QX11Info>
+
+#include "main.h"
+#include "utils.h"
+
+namespace KWin
+{
+
+class X11TestApplication : public Application
+{
+    Q_OBJECT
+public:
+    X11TestApplication(int &argc, char **argv);
+    virtual ~X11TestApplication();
+
+protected:
+    void performStartup() override;
+
+};
+
+X11TestApplication::X11TestApplication(int &argc, char **argv)
+    : Application(OperationModeX11, argc, argv)
+{
+    setX11Connection(QX11Info::connection());
+    setX11RootWindow(QX11Info::appRootWindow());
+}
+
+X11TestApplication::~X11TestApplication()
+{
+}
+
+void X11TestApplication::performStartup()
+{
+}
+
+}
+
+class X11TimestampUpdateTest : public QObject
+{
+    Q_OBJECT
+private Q_SLOTS:
+    void testGrabAfterServerTime();
+    void testBeforeLastGrabTime();
+};
+
+void X11TimestampUpdateTest::testGrabAfterServerTime()
+{
+    // this test tries to grab the X keyboard with a timestamp in future
+    // that should fail, but after updating the X11 timestamp, it should
+    // work again
+    KWin::updateXTime();
+    QCOMPARE(KWin::grabXKeyboard(), true);
+    KWin::ungrabXKeyboard();
+
+    // now let's change the timestamp
+    KWin::kwinApp()->setX11Time(KWin::xTime() + 5 * 60 * 1000);
+
+    // now grab keyboard should fail
+    QCOMPARE(KWin::grabXKeyboard(), false);
+
+    // let's update timestamp, now it should work again
+    KWin::updateXTime();
+    QCOMPARE(KWin::grabXKeyboard(), true);
+    KWin::ungrabXKeyboard();
+}
+
+void X11TimestampUpdateTest::testBeforeLastGrabTime()
+{
+    // this test tries to grab the X keyboard with a timestamp before the
+    // last grab time on the server. That should fail, but after updating the X11
+    // timestamp it should work again
+
+    // first set the grab timestamp
+    KWin::updateXTime();
+    QCOMPARE(KWin::grabXKeyboard(), true);
+    KWin::ungrabXKeyboard();
+
+    // now go to past
+    const auto timestamp = KWin::xTime();
+    KWin::kwinApp()->setX11Time(KWin::xTime() - 5 * 60 * 1000, KWin::Application::TimestampUpdate::Always);
+    QCOMPARE(KWin::xTime(), timestamp - 5 * 60 * 1000);
+
+    // now grab keyboard should fail
+    QCOMPARE(KWin::grabXKeyboard(), false);
+
+    // let's update timestamp, now it should work again
+    KWin::updateXTime();
+    QVERIFY(KWin::xTime() >= timestamp);
+    QCOMPARE(KWin::grabXKeyboard(), true);
+    KWin::ungrabXKeyboard();
+}
+
+int main(int argc, char *argv[])
+{
+    setenv("QT_QPA_PLATFORM", "xcb", true);
+    KWin::X11TestApplication app(argc, argv);
+    app.setAttribute(Qt::AA_Use96Dpi, true);
+    X11TimestampUpdateTest tc;
+    return QTest::qExec(&tc, argc, argv);
+}
+
+#include "test_x11_timestamp_update.moc"
diff --git a/main.h b/main.h
--- a/main.h
+++ b/main.h
@@ -104,8 +104,12 @@
     xcb_timestamp_t x11Time() const {
         return m_x11Time;
     }
-    void setX11Time(xcb_timestamp_t timestamp) {
-        if (timestamp > m_x11Time) {
+    enum class TimestampUpdate {
+        OnlyIfLarger,
+        Always
+    };
+    void setX11Time(xcb_timestamp_t timestamp, TimestampUpdate force = TimestampUpdate::OnlyIfLarger) {
+        if (timestamp > m_x11Time || force == TimestampUpdate::Always) {
             m_x11Time = timestamp;
         }
     }
diff --git a/utils.h b/utils.h
--- a/utils.h
+++ b/utils.h
@@ -143,12 +143,12 @@
 
 template <typename T> using ScopedCPointer = QScopedPointer<T, QScopedPointerPodDeleter>;
 
-void updateXTime();
+void KWIN_EXPORT updateXTime();
 void grabXServer();
 void ungrabXServer();
 bool grabbedXServer();
-bool grabXKeyboard(xcb_window_t w = rootWindow());
-void ungrabXKeyboard();
+bool KWIN_EXPORT grabXKeyboard(xcb_window_t w = rootWindow());
+void KWIN_EXPORT ungrabXKeyboard();
 
 /**
  * Small helper class which performs @link grabXServer in the ctor and
diff --git a/utils.cpp b/utils.cpp
--- a/utils.cpp
+++ b/utils.cpp
@@ -84,7 +84,7 @@
     // NOTE: QX11Info::getTimestamp does not yet search the event queue as the old
     // solution did. This means there might be regressions currently. See the
     // documentation above on how it should be done properly.
-    kwinApp()->setX11Time(QX11Info::getTimestamp());
+    kwinApp()->setX11Time(QX11Info::getTimestamp(), Application::TimestampUpdate::Always);
 }
 
 static int server_grab_count = 0;