diff --git a/abstract_client.cpp b/abstract_client.cpp
index 1d788c2f30..2bc0104efa 100644
--- a/abstract_client.cpp
+++ b/abstract_client.cpp
@@ -43,4 +43,16 @@ bool AbstractClient::isTransient() const
     return false;
 }
 
+TabGroup *AbstractClient::tabGroup() const
+{
+    return nullptr;
+}
+
+bool AbstractClient::untab(const QRect &toGeometry, bool clientRemoved)
+{
+    Q_UNUSED(toGeometry)
+    Q_UNUSED(clientRemoved)
+    return false;
+}
+
 }
diff --git a/abstract_client.h b/abstract_client.h
index 9a1befe32c..12a5afc5f9 100644
--- a/abstract_client.h
+++ b/abstract_client.h
@@ -21,10 +21,13 @@ along with this program.  If not, see <http://www.gnu.org/licenses/>.
 #define KWIN_ABSTRACT_CLIENT_H
 
 #include "toplevel.h"
+#include "options.h"
 
 namespace KWin
 {
 
+class TabGroup;
+
 namespace TabBox
 {
 class TabBoxClientImpl;
@@ -63,6 +66,20 @@ public:
     virtual void sendToScreen(int screen) = 0;
     virtual const QKeySequence &shortcut() const  = 0;
     virtual void setShortcut(const QString &cut) = 0;
+    virtual bool performMouseCommand(Options::MouseCommand, const QPoint &globalPos) = 0;
+    virtual void setOnAllDesktops(bool set) = 0;
+    virtual void minimize(bool avoid_animation = false) = 0;
+    virtual void setFullScreen(bool set, bool user = true) = 0;
+    virtual bool keepAbove() const = 0;
+    virtual void setKeepAbove(bool) = 0;
+    virtual bool keepBelow() const = 0;
+    virtual void setKeepBelow(bool) = 0;
+    virtual TabGroup *tabGroup() const;
+    Q_INVOKABLE virtual bool untab(const QRect &toGeometry = QRect(), bool clientRemoved = false);
+    virtual MaximizeMode maximizeMode() const = 0;
+    virtual void maximize(MaximizeMode) = 0;
+    virtual bool noBorder() const = 0;
+    virtual void setNoBorder(bool set) = 0;
 
     // TODO: remove boolean trap
     static bool belongToSameApplication(const AbstractClient* c1, const AbstractClient* c2, bool active_hack = false);
diff --git a/client.h b/client.h
index 50553c68e9..f643faa442 100644
--- a/client.h
+++ b/client.h
@@ -356,7 +356,7 @@ public:
 
     virtual int desktop() const;
     void setDesktop(int);
-    void setOnAllDesktops(bool set);
+    void setOnAllDesktops(bool set) override;
 
     void sendToScreen(int screen) override;
 
@@ -380,7 +380,7 @@ public:
     bool isMinimized() const override;
     bool isMaximizable() const;
     QRect geometryRestore() const;
-    MaximizeMode maximizeMode() const;
+    MaximizeMode maximizeMode() const override;
 
     enum QuickTileFlag {
         QuickTileNone = 0,
@@ -399,7 +399,7 @@ public:
     void setMaximize(bool vertically, bool horizontally);
     QRect iconGeometry() const;
 
-    void setFullScreen(bool set, bool user = true);
+    void setFullScreen(bool set, bool user = true) override;
     bool isFullScreen() const override;
     bool isFullScreenable(bool fullscreen_hack = false) const;
     bool isActiveFullScreen() const;
@@ -411,8 +411,8 @@ public:
         return fullscreen_mode;    // only for session saving
     }
 
-    bool noBorder() const;
-    void setNoBorder(bool set);
+    bool noBorder() const override;
+    void setNoBorder(bool set) override;
     bool userCanSetNoBorder() const;
     void checkNoBorder();
 
@@ -425,10 +425,10 @@ public:
     bool skipSwitcher() const override;
     void setSkipSwitcher(bool set);
 
-    bool keepAbove() const;
-    void setKeepAbove(bool);
-    bool keepBelow() const;
-    void setKeepBelow(bool);
+    bool keepAbove() const override;
+    void setKeepAbove(bool) override;
+    bool keepBelow() const override;
+    void setKeepBelow(bool) override;
     virtual Layer layer() const;
     Layer belongsToLayer() const;
     void invalidateLayer();
@@ -493,7 +493,7 @@ public:
     void setShortcut(const QString& cut) override;
 
     Options::WindowOperation mouseButtonToWindowOperation(Qt::MouseButtons button);
-    bool performMouseCommand(Options::MouseCommand, const QPoint& globalPos);
+    bool performMouseCommand(Options::MouseCommand, const QPoint& globalPos) override;
 
     QRect adjustedClientArea(const QRect& desktop, const QRect& area) const;
 
@@ -537,10 +537,10 @@ public:
     static bool sameAppWindowRoleMatch(const Client* c1, const Client* c2, bool active_hack);
 
     void setMinimized(bool set);
-    void minimize(bool avoid_animation = false);
+    void minimize(bool avoid_animation = false) override;
     void unminimize(bool avoid_animation = false);
     void killWindow();
-    void maximize(MaximizeMode);
+    void maximize(MaximizeMode) override;
     void toggleShade();
     void showContextHelp();
     void cancelShadeHoverTimer();
@@ -551,7 +551,7 @@ public:
     bool hasStrut() const;
 
     // Tabbing functions
-    TabGroup* tabGroup() const; // Returns a pointer to client_group
+    TabGroup* tabGroup() const override; // Returns a pointer to client_group
     Q_INVOKABLE inline bool tabBefore(Client *other, bool activate) { return tabTo(other, false, activate); }
     Q_INVOKABLE inline bool tabBehind(Client *other, bool activate) { return tabTo(other, true, activate); }
     /**
@@ -566,7 +566,7 @@ public:
      * WARNING: non dynamic properties are ignored - you're not supposed to alter/update such explicitly
      */
     Q_INVOKABLE void syncTabGroupFor(QString property, bool fromThisClient = false);
-    Q_INVOKABLE bool untab(const QRect &toGeometry = QRect(), bool clientRemoved = false);
+    Q_INVOKABLE bool untab(const QRect &toGeometry = QRect(), bool clientRemoved = false) override;
     /**
      * Set tab group - this is to be invoked by TabGroup::add/remove(client) and NO ONE ELSE
      */
diff --git a/useractions.cpp b/useractions.cpp
index 9eee210eac..55d1efb85d 100644
--- a/useractions.cpp
+++ b/useractions.cpp
@@ -735,7 +735,7 @@ void UserActionsMenu::slotWindowOperation(QAction *action)
     qRegisterMetaType<Options::WindowOperation>();
     QMetaObject::invokeMethod(workspace(), "performWindowOperation",
                               Qt::QueuedConnection,
-                              Q_ARG(KWin::Client*, c.data()),
+                              Q_ARG(KWin::AbstractClient*, c.data()),
                               Q_ARG(Options::WindowOperation, op));
 }
 
@@ -1019,7 +1019,7 @@ void Workspace::clientShortcutUpdated(Client* c)
     }
 }
 
-void Workspace::performWindowOperation(Client* c, Options::WindowOperation op)
+void Workspace::performWindowOperation(AbstractClient* c, Options::WindowOperation op)
 {
     if (!c)
         return;
@@ -1107,7 +1107,7 @@ void Workspace::performWindowOperation(Client* c, Options::WindowOperation op)
         break;
     case Options::RemoveTabFromGroupOp:
         if (c->untab(c->geometry().translated(cascadeOffset(c))) && options->focusPolicyIsReasonable())
-             takeActivity(c, ActivityFocus | ActivityRaise);
+             takeActivity(dynamic_cast<Client*>(c), ActivityFocus | ActivityRaise);
         break;
     case Options::ActivateNextTabOp:
         if (c->tabGroup())
diff --git a/workspace.h b/workspace.h
index db369e2681..c5da590c77 100644
--- a/workspace.h
+++ b/workspace.h
@@ -340,7 +340,7 @@ public:
     void unregisterEventFilter(X11EventFilter *filter);
 
 public Q_SLOTS:
-    void performWindowOperation(KWin::Client* c, Options::WindowOperation op);
+    void performWindowOperation(KWin::AbstractClient* c, Options::WindowOperation op);
     // Keybindings
     //void slotSwitchToWindow( int );
     void slotWindowToDesktop();