diff --git a/src/childprocess.cpp b/src/childprocess.cpp
index 1ad43b2d30..49970b45a7 100644
--- a/src/childprocess.cpp
+++ b/src/childprocess.cpp
@@ -92,11 +92,11 @@ qint64 ChildProcessContext::_write(const QString& chunk, const QString& encoding
     QTextCodec* codec = QTextCodec::codecForName(encoding.toLatin1());
 
     // If unavailable, attempt UTF-8 codec
-    if ((QTextCodec*)NULL == codec) {
+    if (!codec) {
         codec = QTextCodec::codecForName("UTF-8");
 
         // Don't even try to write if UTF-8 codec is unavailable
-        if ((QTextCodec*)NULL == codec) {
+        if (!codec) {
             return -1;
         }
     }
diff --git a/src/cookiejar.h b/src/cookiejar.h
index 6fa3c53ca2..49386f625a 100644
--- a/src/cookiejar.h
+++ b/src/cookiejar.h
@@ -43,7 +43,7 @@ class CookieJar : public QNetworkCookieJar {
     Q_PROPERTY(QVariantList cookies READ cookiesToMap WRITE addCookiesFromMap)
 
 public:
-    CookieJar(QString cookiesFile, QObject* parent = NULL);
+    CookieJar(QString cookiesFile, QObject* parent = Q_NULLPTR);
     virtual ~CookieJar();
 
     bool setCookiesFromUrl(const QList<QNetworkCookie>& cookieList, const QUrl& url);
diff --git a/src/encoding.cpp b/src/encoding.cpp
index 1033d0ee42..e117834fbf 100644
--- a/src/encoding.cpp
+++ b/src/encoding.cpp
@@ -35,7 +35,7 @@ Encoding::Encoding()
     QTextCodec* codec = QTextCodec::codecForName(DEFAULT_CODEC_NAME);
 
     // Fall back to locale codec
-    if ((QTextCodec*)NULL == codec) {
+    if (!codec) {
         codec = QTextCodec::codecForLocale();
     }
 
@@ -49,7 +49,11 @@ Encoding::Encoding(const QString& encoding)
 
 Encoding::~Encoding()
 {
-    m_codec = (QTextCodec*)NULL;
+    if (m_codec) {
+        // TODO: Encoding class does not inherit QObject, so
+        // we have to nullifyt m_codec member manually;
+        m_codec = Q_NULLPTR;
+    }
 }
 
 QString Encoding::decode(const QByteArray& bytes) const
@@ -73,7 +77,7 @@ void Encoding::setEncoding(const QString& encoding)
     if (!encoding.isEmpty()) {
         QTextCodec* codec = QTextCodec::codecForName(encoding.toLatin1());
 
-        if ((QTextCodec*)NULL != codec) {
+        if (codec) {
             m_codec = codec;
         }
     }
@@ -86,7 +90,7 @@ QTextCodec* Encoding::getCodec() const
 {
     QTextCodec* codec = m_codec;
 
-    if ((QTextCodec*)NULL == codec) {
+    if (!codec) {
         codec = QTextCodec::codecForLocale();
     }
 
diff --git a/src/env.cpp b/src/env.cpp
index 0c20c42f61..a449ba8d89 100644
--- a/src/env.cpp
+++ b/src/env.cpp
@@ -34,11 +34,11 @@
 #include <QString>
 #include <QVariantMap>
 
-static Env* env_instance = NULL;
+static Env* env_instance = Q_NULLPTR;
 
 Env* Env::instance()
 {
-    if (NULL == env_instance) {
+    if (!env_instance) {
         env_instance = new Env();
     }
 
diff --git a/src/filesystem.cpp b/src/filesystem.cpp
index 16a7d6ffe7..70e7595c92 100644
--- a/src/filesystem.cpp
+++ b/src/filesystem.cpp
@@ -216,7 +216,7 @@ void File::close()
     if (m_file) {
         m_file->close();
         delete m_file;
-        m_file = NULL;
+        m_file = Q_NULLPTR;
     }
     deleteLater();
 }
@@ -228,7 +228,7 @@ bool File::setEncoding(const QString& encoding)
     }
 
     // "Binary" mode doesn't use/need text codecs
-    if ((QTextStream*)NULL == m_fileStream) {
+    if (!m_fileStream) {
         // TODO: Should we switch to "text" mode?
         return false;
     }
@@ -237,7 +237,7 @@ bool File::setEncoding(const QString& encoding)
     // "utf-8"), we need to get the codec in the system first and use its
     // canonical name
     QTextCodec* codec = QTextCodec::codecForName(encoding.toLatin1());
-    if ((QTextCodec*)NULL == codec) {
+    if (!codec) {
         return false;
     }
 
@@ -258,7 +258,7 @@ QString File::getEncoding() const
 {
     QString encoding;
 
-    if ((QTextStream*)NULL != m_fileStream) {
+    if (m_fileStream) {
         encoding = QString(m_fileStream->codec()->name());
     }
 
diff --git a/src/networkaccessmanager.cpp b/src/networkaccessmanager.cpp
index b5faadd009..ac539c3e8c 100644
--- a/src/networkaccessmanager.cpp
+++ b/src/networkaccessmanager.cpp
@@ -49,7 +49,7 @@ const qint64 MAX_REQUEST_POST_BODY_SIZE = 10 * 1000 * 1000;
 
 static const char* toString(QNetworkAccessManager::Operation op)
 {
-    const char* str = 0;
+    const char* str = Q_NULLPTR;
     switch (op) {
     case QNetworkAccessManager::HeadOperation:
         str = "HEAD";
@@ -157,7 +157,7 @@ NetworkAccessManager::NetworkAccessManager(QObject* parent, const Config* config
     , m_maxAuthAttempts(3)
     , m_resourceTimeout(0)
     , m_idCounter(0)
-    , m_networkDiskCache(0)
+    , m_networkDiskCache(Q_NULLPTR)
     , m_sslConfiguration(QSslConfiguration::defaultConfiguration())
 {
     if (config->diskCacheEnabled()) {
@@ -242,7 +242,7 @@ void NetworkAccessManager::prepareSslConfiguration(const Config* config)
             m_sslConfiguration.setCaCertificates(caCerts);
             m_sslConfiguration.setLocalCertificate(clientCert);
 
-            QFile* keyFile = NULL;
+            QFile* keyFile = Q_NULLPTR;
             if (config->sslClientKeyFile().isEmpty()) {
                 keyFile = new QFile(config->sslClientCertificateFile());
             } else {
diff --git a/src/phantom.cpp b/src/phantom.cpp
index 12d5bcb67a..7744b08007 100644
--- a/src/phantom.cpp
+++ b/src/phantom.cpp
@@ -57,7 +57,7 @@
 #error "This version of QtWebKit is not supported. Please use QtWebKit >= 5.212"
 #endif
 
-static Phantom* phantomInstance = NULL;
+static Phantom* phantomInstance = Q_NULLPTR;
 
 // private:
 Phantom::Phantom(QObject* parent)
@@ -157,7 +157,7 @@ void Phantom::init()
 // public:
 Phantom* Phantom::instance()
 {
-    if (NULL == phantomInstance) {
+    if (!phantomInstance) {
         phantomInstance = new Phantom();
         phantomInstance->init();
     }
@@ -405,7 +405,7 @@ QString Phantom::proxy()
 {
     QNetworkProxy proxy = QNetworkProxy::applicationProxy();
     if (proxy.hostName().isEmpty()) {
-        return NULL;
+        return QString();
     }
     return proxy.hostName() + ":" + QString::number(proxy.port());
 }
diff --git a/src/phantom.h b/src/phantom.h
index a509ee2888..e36f233476 100644
--- a/src/phantom.h
+++ b/src/phantom.h
@@ -167,7 +167,7 @@ public slots:
      * @param port The proxy port
      * @param proxyType The type of this proxy
      */
-    void setProxy(const QString& ip, const qint64& port = 80, const QString& proxyType = "http", const QString& user = NULL, const QString& password = NULL);
+    void setProxy(const QString& ip, const qint64& port = 80, const QString& proxyType = "http", const QString& user = QString(), const QString& password = QString());
 
     QString proxy();
 
diff --git a/src/repl.cpp b/src/repl.cpp
index 01474f5e1e..da1c15db55 100644
--- a/src/repl.cpp
+++ b/src/repl.cpp
@@ -66,12 +66,12 @@
 // public:
 bool REPL::instanceExists()
 {
-    return REPL::getInstance() != NULL;
+    return REPL::getInstance() != Q_NULLPTR;
 }
 
 REPL* REPL::getInstance(QWebFrame* webframe, Phantom* parent)
 {
-    static REPL* singleton = NULL;
+    static REPL* singleton = Q_NULLPTR;
     if (!singleton && webframe && parent) {
         // This will create the singleton only when all the parameters are given
         singleton = new REPL(webframe, parent);
@@ -202,7 +202,7 @@ void REPL::startLoop()
 
     // Load REPL history
     linenoiseHistoryLoad(m_historyFilepath.data()); //< requires "char *"
-    while (m_looping && (userInput = linenoise(PROMPT)) != NULL) {
+    while (m_looping && (userInput = linenoise(PROMPT)) != Q_NULLPTR) {
         if (userInput[0] != '\0') {
             // Send the user input to the main Phantom frame for evaluation
             m_webframe->evaluateJavaScript(
diff --git a/src/system.cpp b/src/system.cpp
index f83daa18a5..18c670935b 100644
--- a/src/system.cpp
+++ b/src/system.cpp
@@ -54,9 +54,9 @@ QString getOSRelease()
 
 System::System(QObject* parent)
     : QObject(parent)
-    , m_stdout((File*)NULL)
-    , m_stderr((File*)NULL)
-    , m_stdin((File*)NULL)
+    , m_stdout(Q_NULLPTR)
+    , m_stderr(Q_NULLPTR)
+    , m_stdin(Q_NULLPTR)
 {
     // Populate "env"
     m_env = Env::instance()->asVariantMap();
@@ -165,17 +165,17 @@ System::System(QObject* parent)
 System::~System()
 {
     // Clean-up standard streams
-    if ((File*)NULL != m_stdout) {
+    if (m_stdout) {
         delete m_stdout;
-        m_stdout = (File*)NULL;
+        m_stdout = Q_NULLPTR;
     }
-    if ((File*)NULL != m_stderr) {
+    if (m_stderr) {
         delete m_stderr;
-        m_stderr = (File*)NULL;
+        m_stderr = Q_NULLPTR;
     }
-    if ((File*)NULL != m_stdin) {
+    if (m_stdin) {
         delete m_stdin;
-        m_stdin = (File*)NULL;
+        m_stdin = Q_NULLPTR;
     }
 }
 
@@ -211,7 +211,7 @@ bool System::isSSLSupported() const
 
 QObject* System::_stdout()
 {
-    if ((File*)NULL == m_stdout) {
+    if (!m_stdout) {
         QFile* f = new QFile();
         f->open(stdout, QIODevice::WriteOnly | QIODevice::Unbuffered);
         m_stdout = createFileInstance(f);
@@ -222,7 +222,7 @@ QObject* System::_stdout()
 
 QObject* System::_stderr()
 {
-    if ((File*)NULL == m_stderr) {
+    if (!m_stderr) {
         QFile* f = new QFile();
         f->open(stderr, QIODevice::WriteOnly | QIODevice::Unbuffered);
         m_stderr = createFileInstance(f);
@@ -233,7 +233,7 @@ QObject* System::_stderr()
 
 QObject* System::_stdin()
 {
-    if ((File*)NULL == m_stdin) {
+    if (!m_stdin) {
         QFile* f = new QFile();
         f->open(stdin, QIODevice::ReadOnly | QIODevice::Unbuffered);
         m_stdin = createFileInstance(f);
@@ -246,15 +246,15 @@ QObject* System::_stdin()
 
 void System::_onTerminalEncodingChanged(const QString& encoding)
 {
-    if ((File*)NULL != m_stdin) {
+    if (!m_stdin) {
         m_stdin->setEncoding(encoding);
     }
 
-    if ((File*)NULL != m_stdout) {
+    if (!m_stdout) {
         m_stdout->setEncoding(encoding);
     }
 
-    if ((File*)NULL != m_stderr) {
+    if (!m_stderr) {
         m_stderr->setEncoding(encoding);
     }
 }
diff --git a/src/webpage.cpp b/src/webpage.cpp
index 3bc6e45ea1..f74d3c5522 100644
--- a/src/webpage.cpp
+++ b/src/webpage.cpp
@@ -89,7 +89,7 @@ class CustomPage : public QWebPage {
     Q_OBJECT
 
 public:
-    CustomPage(WebPage* parent = 0)
+    CustomPage(WebPage* parent = Q_NULLPTR)
         : QWebPage(parent)
         , m_webPage(parent)
     {
@@ -265,13 +265,13 @@ class WebpageCallbacks : public QObject {
     Q_OBJECT
 
 public:
-    WebpageCallbacks(QObject* parent = 0)
+    WebpageCallbacks(QObject* parent = Q_NULLPTR)
         : QObject(parent)
-        , m_genericCallback(NULL)
-        , m_filePickerCallback(NULL)
-        , m_jsConfirmCallback(NULL)
-        , m_jsPromptCallback(NULL)
-        , m_jsInterruptCallback(NULL)
+        , m_genericCallback(Q_NULLPTR)
+        , m_filePickerCallback(Q_NULLPTR)
+        , m_jsConfirmCallback(Q_NULLPTR)
+        , m_jsPromptCallback(Q_NULLPTR)
+        , m_jsInterruptCallback(Q_NULLPTR)
     {
     }
 
@@ -1603,7 +1603,7 @@ QObject* WebPage::getPage(const QString& windowName) const
             return childPages.at(i);
         }
     }
-    return NULL;
+    return Q_NULLPTR;
 }
 
 bool WebPage::ownsPages() const
@@ -1720,7 +1720,7 @@ void WebPage::switchToMainFrame()
 
 bool WebPage::switchToParentFrame()
 {
-    if (m_currentFrame->parentFrame() != NULL) {
+    if (m_currentFrame->parentFrame()) {
         this->changeCurrentFrame(m_currentFrame->parentFrame());
         return true;
     }
@@ -1759,10 +1759,10 @@ static void injectCallbacksObjIntoFrame(QWebFrame* frame, WebpageCallbacks* call
 
 void WebPage::setupFrame(QWebFrame* frame)
 {
-    qDebug() << "WebPage - setupFrame" << (frame == NULL ? "" : frame->frameName());
+    qDebug() << "WebPage - setupFrame" << (frame == Q_NULLPTR ? "" : frame->frameName());
 
     // Inject the Callbacks object in the main frame
-    injectCallbacksObjIntoFrame(frame == NULL ? m_mainFrame : frame, m_callbacks);
+    injectCallbacksObjIntoFrame(frame == Q_NULLPTR ? m_mainFrame : frame, m_callbacks);
 }
 
 void WebPage::updateLoadingProgress(int progress)
diff --git a/src/webpage.h b/src/webpage.h
index 3559be83ef..633c038d8b 100644
--- a/src/webpage.h
+++ b/src/webpage.h
@@ -275,7 +275,7 @@ public slots:
      * @brief getPage
      * @param windowName
      * @return Returns the page that matches <code>'window.name'</code>,
-     *         or NULL if none is found
+     *         or Q_NULLPTR if none is found
      */
     QObject* getPage(const QString& windowName) const;
 
@@ -507,7 +507,7 @@ public slots:
 
 private slots:
     void finish(bool ok);
-    void setupFrame(QWebFrame* frame = NULL);
+    void setupFrame(QWebFrame* frame = Q_NULLPTR);
     void updateLoadingProgress(int progress);
     void handleRepaintRequested(const QRect& dirtyRect);
     void handleUrlChanged(const QUrl& url);
diff --git a/src/webserver.cpp b/src/webserver.cpp
index d82681b46d..5f80ee7134 100644
--- a/src/webserver.cpp
+++ b/src/webserver.cpp
@@ -119,7 +119,7 @@ bool WebServer::listenOnPort(const QString& port, const QVariantMap& opts)
         options << "enable_keep_alive"
                 << "yes";
     }
-    options << NULL;
+    options << 0;
 
     // Start the server
     m_ctx = mg_start(&callback, this, options.data());