diff --git a/autotests/integration/x11_client_test.cpp b/autotests/integration/x11_client_test.cpp
--- a/autotests/integration/x11_client_test.cpp
+++ b/autotests/integration/x11_client_test.cpp
@@ -50,6 +50,7 @@
     void cleanup();
 
     void testCaptionSimplified();
+    void testCaptionNonPrintable();
     void testFullscreenLayerWithActiveWaylandWindow();
     void testFocusInWithWaylandLastActiveWindow();
     void testX11WindowId();
@@ -145,6 +146,58 @@
     c.reset();
 }
 
+void X11ClientTest::testCaptionNonPrintable()
+{
+    // this test verifies that non-printable characters in captions get stripped
+    // but printable non-BMP characters, such as Emoji, are kept
+    // BUG: 376813
+    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("\bTesting non\302\255printable:\177, emoij:\360\237\230\203, non-characters:\357\277\276");
+    const QByteArray expectedTitle = QByteArrayLiteral("Testing nonprintable:, emoij:\360\237\230\203, non-characters:");
+    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);
+    QVERIFY(client->caption() != QString::fromUtf8(origTitle));
+    QCOMPARE(client->caption(), QString::fromUtf8(expectedTitle);
+
+    // 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();
+}
+
 void X11ClientTest::testFullscreenLayerWithActiveWaylandWindow()
 {
     // this test verifies that an X11 fullscreen window does not stay in the active layer
diff --git a/client.cpp b/client.cpp
--- a/client.cpp
+++ b/client.cpp
@@ -1463,13 +1463,26 @@
 
 void Client::setCaption(const QString& _s, bool force)
 {
-    if (!force && _s == cap_normal)
-        return;
     QString s(_s);
-    for (int i = 0; i < s.length(); ++i)
-        if (!s[i].isPrint())
-            s[i] = QChar(u' ');
+    for (int i = 0; i < s.length(); ) {
+        if (!s[i].isPrint()) {
+            if (QChar(s[i]).isHighSurrogate() && i + 1 < s.length() && QChar(s[i + 1]).isLowSurrogate()) {
+                const uint uc = QChar::surrogateToUcs4(s[i], s[i + 1]);
+                if (!QChar::isPrint(uc)) {
+                    s.remove(i, 2);
+                } else {
+                    i += 2;
+                }
+                continue;
+            }
+            s.remove(i, 1);
+            continue;
+        }
+        ++i;
+    }
     const bool changed = (s != cap_normal);
+    if (!force && !changed)
+        return;
     cap_normal = s;
     if (!force && !changed) {
         emit captionChanged();