diff --git a/tabbox/tabbox.cpp b/tabbox/tabbox.cpp
index c5d53dce92..f397d791f4 100644
--- a/tabbox/tabbox.cpp
+++ b/tabbox/tabbox.cpp
@@ -777,7 +777,9 @@ void TabBox::hide(bool abort)
     if (isDisplayed())
         qCDebug(KWIN_TABBOX) << "Tab box was not properly closed by an effect";
     m_tabBox->hide(abort);
-    Xcb::sync();
+    if (kwinApp()->x11Connection()) {
+        Xcb::sync();
+    }
 }
 
 void TabBox::reconfigure()
diff --git a/tabbox/tabboxhandler.cpp b/tabbox/tabboxhandler.cpp
index 9edfca2e54..9d8f16ce78 100644
--- a/tabbox/tabboxhandler.cpp
+++ b/tabbox/tabboxhandler.cpp
@@ -384,7 +384,9 @@ void TabBoxHandler::show()
         d->show();
     }
     if (d->config.isHighlightWindows()) {
-        Xcb::sync();
+        if (kwinApp()->x11Connection()) {
+            Xcb::sync();
+        }
         // TODO this should be
         // QMetaObject::invokeMethod(this, "initHighlightWindows", Qt::QueuedConnection);
         // but we somehow need to cross > 1 event cycle (likely because of queued invocation in the effects)