diff --git a/client.cpp b/client.cpp
index 5c49b1691d..2e6966643e 100644
--- a/client.cpp
+++ b/client.cpp
@@ -630,6 +630,11 @@ void Client::updateShape()
 
 static Xcb::Window shape_helper_window(XCB_WINDOW_NONE);
 
+void Client::cleanupX11()
+{
+    shape_helper_window.reset();
+}
+
 void Client::updateInputShape()
 {
     if (hiddenPreview())   // Sets it to none, don't change
diff --git a/client.h b/client.h
index 7a28b547ba..08e25abe3a 100644
--- a/client.h
+++ b/client.h
@@ -355,6 +355,8 @@ public:
      **/
     void showOnScreenEdge();
 
+    static void cleanupX11();
+
 public Q_SLOTS:
     void closeWindow() override;
     void updateCaption();
diff --git a/libkwineffects/kwinglobals.h b/libkwineffects/kwinglobals.h
index 18b78f44e7..3ae0d36b54 100644
--- a/libkwineffects/kwinglobals.h
+++ b/libkwineffects/kwinglobals.h
@@ -144,6 +144,7 @@ KWIN_EXPORT xcb_connection_t *connection()
     if (!s_con) {
         s_con = reinterpret_cast<xcb_connection_t*>(qApp->property("x11Connection").value<void*>());
     }
+    Q_ASSERT(qApp);
     return s_con;
 }
 
diff --git a/workspace.cpp b/workspace.cpp
index a179a198db..a179889b22 100644
--- a/workspace.cpp
+++ b/workspace.cpp
@@ -448,6 +448,7 @@ Workspace::~Workspace()
         m_allClients.removeAll(c);
         desktops.removeAll(c);
     }
+    Client::cleanupX11();
     for (UnmanagedList::iterator it = unmanaged.begin(), end = unmanaged.end(); it != end; ++it)
         (*it)->release(ReleaseReason::KWinShutsDown);
     xcb_delete_property(connection(), rootWindow(), atoms->kwin_running);