diff --git a/tabbox/clientmodel.cpp b/tabbox/clientmodel.cpp
index ce29236562..d060c09c5a 100644
--- a/tabbox/clientmodel.cpp
+++ b/tabbox/clientmodel.cpp
@@ -213,7 +213,7 @@ void ClientModel::createClientList(int desktop, bool partialReset)
                 }
             }
             if (index >= stacking.size() - 1) {
-                c = NULL;
+                c = nullptr;
             } else {
                 c = stacking[++index].data();
             }
diff --git a/tabbox/clientmodel.h b/tabbox/clientmodel.h
index 0bfe97f4ac..f08295f4f2 100644
--- a/tabbox/clientmodel.h
+++ b/tabbox/clientmodel.h
@@ -57,7 +57,7 @@ public:
         MinimizedRole = Qt::UserRole + 6, ///< TabBoxClient is minimized
         CloseableRole = Qt::UserRole + 7 ///< TabBoxClient can be closed
     };
-    explicit ClientModel(QObject* parent = 0);
+    explicit ClientModel(QObject* parent = nullptr);
     ~ClientModel();
     virtual QVariant data(const QModelIndex& index, int role = Qt::DisplayRole) const;
     virtual int columnCount(const QModelIndex& parent = QModelIndex()) const;
diff --git a/tabbox/desktopchain.h b/tabbox/desktopchain.h
index ceeeb977a9..e2505c9c19 100644
--- a/tabbox/desktopchain.h
+++ b/tabbox/desktopchain.h
@@ -88,7 +88,7 @@ class DesktopChainManager : public QObject
     Q_OBJECT
 
 public:
-    explicit DesktopChainManager(QObject *parent = 0);
+    explicit DesktopChainManager(QObject *parent = nullptr);
     virtual ~DesktopChainManager();
 
     /**
diff --git a/tabbox/desktopmodel.h b/tabbox/desktopmodel.h
index a069e47092..e154140dde 100644
--- a/tabbox/desktopmodel.h
+++ b/tabbox/desktopmodel.h
@@ -51,7 +51,7 @@ public:
         DesktopNameRole = Qt::UserRole + 1, ///< Desktop name
         ClientModelRole = Qt::UserRole + 2 ///< Clients on this desktop
     };
-    explicit DesktopModel(QObject* parent = 0);
+    explicit DesktopModel(QObject* parent = nullptr);
     ~DesktopModel();
 
     virtual QVariant data(const QModelIndex& index, int role = Qt::DisplayRole) const;
diff --git a/tabbox/tabbox.cpp b/tabbox/tabbox.cpp
index 9969d37818..ce15837aea 100644
--- a/tabbox/tabbox.cpp
+++ b/tabbox/tabbox.cpp
@@ -249,7 +249,7 @@ QWeakPointer<TabBoxClient> TabBoxHandlerImpl::clientToAddToList(TabBoxClient* cl
     if (!client) {
         return QWeakPointer<TabBoxClient>();
     }
-    Client* ret = NULL;
+    Client* ret = nullptr;
     Client* current = (static_cast< TabBoxClientImpl* >(client))->client();
 
     bool addClient = checkDesktop(client, desktop)
@@ -261,7 +261,7 @@ QWeakPointer<TabBoxClient> TabBoxHandlerImpl::clientToAddToList(TabBoxClient* cl
     if (addClient) {
         // don't add windows that have modal dialogs
         Client* modal = current->findModal();
-        if (modal == NULL || modal == current)
+        if (modal == nullptr || modal == current)
             ret = current;
         else if (!clientList().contains(modal->tabBoxClient()))
             ret = modal;
@@ -405,7 +405,7 @@ bool TabBoxClientImpl::isFirstInTabBox() const
 /*********************************************************
 * TabBox
 *********************************************************/
-TabBox *TabBox::s_self = NULL;
+TabBox *TabBox::s_self = nullptr;
 
 TabBox *TabBox::create(QObject *parent)
 {
@@ -474,7 +474,7 @@ TabBox::TabBox(QObject *parent)
 TabBox::~TabBox()
 {
     QDBusConnection::sessionBus().unregisterObject(QStringLiteral("/TabBox"));
-    s_self = NULL;
+    s_self = nullptr;
 }
 
 void TabBox::handlerReady()
@@ -635,10 +635,10 @@ Client* TabBox::currentClient()
 {
     if (TabBoxClientImpl* client = static_cast< TabBoxClientImpl* >(m_tabBox->client(m_tabBox->currentIndex()))) {
         if (!Workspace::self()->hasClient(client->client()))
-            return NULL;
+            return nullptr;
         return client->client();
     } else
-        return NULL;
+        return nullptr;
 }
 
 /*!
@@ -1202,7 +1202,7 @@ void TabBox::walkThroughDesktops(bool forward)
 
 void TabBox::CDEWalkThroughWindows(bool forward)
 {
-    Client* c = NULL;
+    Client* c = nullptr;
 // this function find the first suitable client for unreasonable focus
 // policies - the topmost one, with some exceptions (can't be keepabove/below,
 // otherwise it gets stuck on them)
@@ -1225,7 +1225,7 @@ void TabBox::CDEWalkThroughWindows(bool forward)
         options_traverse_all = group.readEntry("TraverseAll", false);
     }
 
-    Client* firstClient = 0;
+    Client* firstClient = nullptr;
     do {
         nc = forward ? nextClientStatic(nc) : previousClientStatic(nc);
         if (!firstClient) {
@@ -1234,7 +1234,7 @@ void TabBox::CDEWalkThroughWindows(bool forward)
             firstClient = nc;
         } else if (nc == firstClient) {
             // No candidates found.
-            nc = 0;
+            nc = nullptr;
             break;
         }
     } while (nc && nc != c &&
@@ -1581,7 +1581,7 @@ bool TabBox::establishTabBoxGrab()
     // the active client, which may not have it.
     assert(!m_forcedGlobalMouseGrab);
     m_forcedGlobalMouseGrab = true;
-    if (Workspace::self()->activeClient() != NULL)
+    if (Workspace::self()->activeClient() != nullptr)
         Workspace::self()->activeClient()->updateMouseGrab();
     return true;
 }
@@ -1592,7 +1592,7 @@ void TabBox::removeTabBoxGrab()
     ungrabXKeyboard();
     assert(m_forcedGlobalMouseGrab);
     m_forcedGlobalMouseGrab = false;
-    if (Workspace::self()->activeClient() != NULL)
+    if (Workspace::self()->activeClient() != nullptr)
         Workspace::self()->activeClient()->updateMouseGrab();
 }
 } // namespace TabBox
diff --git a/tabbox/tabboxhandler.cpp b/tabbox/tabboxhandler.cpp
index 8514e06c90..6542374893 100644
--- a/tabbox/tabboxhandler.cpp
+++ b/tabbox/tabboxhandler.cpp
@@ -113,8 +113,8 @@ TabBoxHandlerPrivate::TabBoxHandlerPrivate(TabBoxHandler *q)
 {
     this->q = q;
     isShown = false;
-    lastRaisedClient = 0;
-    lastRaisedClientSucc = 0;
+    lastRaisedClient = nullptr;
+    lastRaisedClientSucc = nullptr;
     config = TabBoxConfig();
     m_clientModel = new ClientModel(q);
     m_desktopModel = new DesktopModel(q);
@@ -197,7 +197,7 @@ void TabBoxHandlerPrivate::updateHighlightWindows()
                     break;
                 }
             }
-            lastRaisedClientSucc = (succIdx < order.count()) ? order.at(succIdx).data() : 0;
+            lastRaisedClientSucc = (succIdx < order.count()) ? order.at(succIdx).data() : nullptr;
             q->raiseClient(lastRaisedClient);
         }
     }
@@ -225,8 +225,8 @@ void TabBoxHandlerPrivate::endHighlightWindows(bool abort)
         q->elevateClient(currentClient, w ? w->winId() : 0, false);
     if (abort && lastRaisedClient && lastRaisedClientSucc)
         q->restack(lastRaisedClient, lastRaisedClientSucc);
-    lastRaisedClient = 0;
-    lastRaisedClientSucc = 0;
+    lastRaisedClient = nullptr;
+    lastRaisedClientSucc = nullptr;
     // highlight windows
     xcb_delete_property(connection(), config.isShowTabBox() && w ? w->winId() : rootWindow(), m_highlightWindowsAtom);
 }
@@ -361,8 +361,8 @@ void TabBoxHandler::setConfig(const TabBoxConfig& config)
 void TabBoxHandler::show()
 {
     d->isShown = true;
-    d->lastRaisedClient = 0;
-    d->lastRaisedClientSucc = 0;
+    d->lastRaisedClient = nullptr;
+    d->lastRaisedClientSucc = nullptr;
     if (d->config.isShowTabBox()) {
         d->show();
     }
@@ -531,7 +531,7 @@ TabBoxClient* TabBoxHandler::client(const QModelIndex& index) const
 {
     if ((!index.isValid()) ||
             (d->config.tabBoxMode() != TabBoxConfig::ClientTabBox))
-        return NULL;
+        return nullptr;
     TabBoxClient* c = static_cast< TabBoxClient* >(
                           d->clientModel()->data(index, ClientModel::ClientRole).value<void *>());
     return c;
@@ -558,9 +558,9 @@ void TabBoxHandler::createModel(bool partialReset)
             }
         }
         if (d->lastRaisedClient && !lastRaised)
-            d->lastRaisedClient = 0;
+            d->lastRaisedClient = nullptr;
         if (d->lastRaisedClientSucc && !lastRaisedSucc)
-            d->lastRaisedClientSucc = 0;
+            d->lastRaisedClientSucc = nullptr;
         break;
     }
     case TabBoxConfig::DesktopTabBox:
@@ -637,7 +637,7 @@ void TabBoxHandler::resetEmbedded()
     emit embeddedChanged(false);
 }
 
-TabBoxHandler* tabBox = 0;
+TabBoxHandler* tabBox = nullptr;
 
 TabBoxClient::TabBoxClient()
 {