diff --git a/src/libs/qmldebug/baseenginedebugclient.cpp b/src/libs/qmldebug/baseenginedebugclient.cpp
index f3e5271e32b..df014e43a00 100644
--- a/src/libs/qmldebug/baseenginedebugclient.cpp
+++ b/src/libs/qmldebug/baseenginedebugclient.cpp
@@ -178,7 +178,7 @@ void BaseEngineDebugClient::stateChanged(State state)
 
 void BaseEngineDebugClient::messageReceived(const QByteArray &data)
 {
-    QPacket ds(connection()->currentDataStreamVersion(), data);
+    QPacket ds(dataStreamVersion(), data);
     int queryId;
     QByteArray type;
     ds >> type >> queryId;
@@ -251,7 +251,7 @@ quint32 BaseEngineDebugClient::addWatch(const PropertyReference &property)
     quint32 id = 0;
     if (state() == Enabled) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("WATCH_PROPERTY") << id << property.m_objectDebugId
            << property.m_name.toUtf8();
         sendMessage(ds.data());
@@ -272,7 +272,7 @@ quint32 BaseEngineDebugClient::addWatch(const ObjectReference &object,
     quint32 id = 0;
     if (state() == Enabled) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("WATCH_EXPR_OBJECT") << id << object.m_debugId << expr;
         sendMessage(ds.data());
     }
@@ -284,7 +284,7 @@ quint32 BaseEngineDebugClient::addWatch(int objectDebugId)
     quint32 id = 0;
     if (state() == Enabled) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("WATCH_OBJECT") << id << objectDebugId;
         sendMessage(ds.data());
     }
@@ -300,7 +300,7 @@ quint32 BaseEngineDebugClient::addWatch(const FileReference &/*file*/)
 void BaseEngineDebugClient::removeWatch(quint32 id)
 {
     if (state() == Enabled) {
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("NO_WATCH") << id;
         sendMessage(ds.data());
     }
@@ -311,7 +311,7 @@ quint32 BaseEngineDebugClient::queryAvailableEngines()
     quint32 id = 0;
     if (state() == Enabled) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("LIST_ENGINES") << id;
         sendMessage(ds.data());
     }
@@ -323,7 +323,7 @@ quint32 BaseEngineDebugClient::queryRootContexts(const EngineReference &engine)
     quint32 id = 0;
     if (state() == Enabled && engine.m_debugId != -1) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("LIST_OBJECTS") << id << engine.m_debugId;
         sendMessage(ds.data());
     }
@@ -335,7 +335,7 @@ quint32 BaseEngineDebugClient::queryObject(int objectId)
     quint32 id = 0;
     if (state() == Enabled && objectId != -1) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("FETCH_OBJECT") << id << objectId << false <<
               true;
         sendMessage(ds.data());
@@ -348,7 +348,7 @@ quint32 BaseEngineDebugClient::queryObjectRecursive(int objectId)
     quint32 id = 0;
     if (state() == Enabled && objectId != -1) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("FETCH_OBJECT") << id << objectId << true <<
               true;
         sendMessage(ds.data());
@@ -363,7 +363,7 @@ quint32 BaseEngineDebugClient::queryExpressionResult(int objectDebugId,
     quint32 id = 0;
     if (state() == Enabled && objectDebugId != -1) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("EVAL_EXPRESSION") << id << objectDebugId << expr
            << engineId;
         sendMessage(ds.data());
@@ -381,7 +381,7 @@ quint32 BaseEngineDebugClient::setBindingForObject(
     quint32 id = 0;
     if (state() == Enabled && objectDebugId != -1) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("SET_BINDING") << id << objectDebugId << propertyName
            << bindingExpression << isLiteralValue << source << line;
         sendMessage(ds.data());
@@ -396,7 +396,7 @@ quint32 BaseEngineDebugClient::resetBindingForObject(
     quint32 id = 0;
     if (state() == Enabled && objectDebugId != -1) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("RESET_BINDING") << id << objectDebugId << propertyName;
         sendMessage(ds.data());
     }
@@ -410,7 +410,7 @@ quint32 BaseEngineDebugClient::setMethodBody(
     quint32 id = 0;
     if (state() == Enabled && objectDebugId != -1) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("SET_METHOD_BODY") << id << objectDebugId
            << methodName << methodBody;
         sendMessage(ds.data());
@@ -424,7 +424,7 @@ quint32 BaseEngineDebugClient::queryObjectsForLocation(
     quint32 id = 0;
     if (state() == Enabled) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("FETCH_OBJECTS_FOR_LOCATION") << id <<
               fileName << lineNumber << columnNumber << false <<
               true;
diff --git a/src/libs/qmldebug/declarativeenginedebugclient.cpp b/src/libs/qmldebug/declarativeenginedebugclient.cpp
index e014aa44fac..21a13a960d3 100644
--- a/src/libs/qmldebug/declarativeenginedebugclient.cpp
+++ b/src/libs/qmldebug/declarativeenginedebugclient.cpp
@@ -46,7 +46,7 @@ quint32 DeclarativeEngineDebugClient::setBindingForObject(
     quint32 id = 0;
     if (state() == Enabled && objectDebugId != -1) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("SET_BINDING") << objectDebugId << propertyName
            << bindingExpression << isLiteralValue << source << line;
         sendMessage(ds.data());
@@ -61,7 +61,7 @@ quint32 DeclarativeEngineDebugClient::resetBindingForObject(
     quint32 id = 0;
     if (state() == Enabled && objectDebugId != -1) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("RESET_BINDING") << objectDebugId << propertyName;
         sendMessage(ds.data());
     }
@@ -75,7 +75,7 @@ quint32 DeclarativeEngineDebugClient::setMethodBody(
     quint32 id = 0;
     if (state() == Enabled && objectDebugId != -1) {
         id = getId();
-        QPacket ds(connection()->currentDataStreamVersion());
+        QPacket ds(dataStreamVersion());
         ds << QByteArray("SET_METHOD_BODY") << objectDebugId
            << methodName << methodBody;
         sendMessage(ds.data());
@@ -85,7 +85,7 @@ quint32 DeclarativeEngineDebugClient::setMethodBody(
 
 void DeclarativeEngineDebugClient::messageReceived(const QByteArray &data)
 {
-    QPacket ds(connection()->currentDataStreamVersion(), data);
+    QPacket ds(dataStreamVersion(), data);
     QByteArray type;
     ds >> type;
 
diff --git a/src/libs/qmldebug/qmldebugclient.cpp b/src/libs/qmldebug/qmldebugclient.cpp
index 5935fee5d25..1b27ee2a125 100644
--- a/src/libs/qmldebug/qmldebugclient.cpp
+++ b/src/libs/qmldebug/qmldebugclient.cpp
@@ -38,6 +38,7 @@
 namespace QmlDebug {
 
 const int protocolVersion = 1;
+const int minimumDataStreamVersion = QDataStream::Qt_4_7;
 
 const QString serverId = QLatin1String("QDeclarativeDebugServer");
 const QString clientId = QLatin1String("QDeclarativeDebugClient");
@@ -86,7 +87,7 @@ static QString socketErrorToString(QAbstractSocket::SocketError error)
 
 QmlDebugConnectionPrivate::QmlDebugConnectionPrivate() :
     protocol(0), server(0), device(0), gotHello(false),
-    currentDataStreamVersion(QDataStream::Qt_4_7),
+    currentDataStreamVersion(minimumDataStreamVersion),
     maximumDataStreamVersion(QDataStream::Qt_DefaultCompiledVersion)
 {
 }
@@ -493,6 +494,12 @@ QmlDebugConnection *QmlDebugClient::connection() const
     return d->connection;
 }
 
+int QmlDebugClient::dataStreamVersion() const
+{
+    Q_D(const QmlDebugClient);
+    return (d->connection ? d->connection->currentDataStreamVersion() : minimumDataStreamVersion);
+}
+
 void QmlDebugClient::sendMessage(const QByteArray &message)
 {
     Q_D(QmlDebugClient);
diff --git a/src/libs/qmldebug/qmldebugclient.h b/src/libs/qmldebug/qmldebugclient.h
index 8d2f5712753..b39ec5f3db4 100644
--- a/src/libs/qmldebug/qmldebugclient.h
+++ b/src/libs/qmldebug/qmldebugclient.h
@@ -95,6 +95,7 @@ public:
     float serviceVersion() const;
     State state() const;
     QmlDebugConnection *connection() const;
+    int dataStreamVersion() const;
 
     virtual void sendMessage(const QByteArray &);
     virtual void stateChanged(State);
diff --git a/src/libs/qmldebug/qmltoolsclient.cpp b/src/libs/qmldebug/qmltoolsclient.cpp
index 7ce05ef71aa..e882f0733b3 100644
--- a/src/libs/qmldebug/qmltoolsclient.cpp
+++ b/src/libs/qmldebug/qmltoolsclient.cpp
@@ -55,7 +55,7 @@ QmlToolsClient::QmlToolsClient(QmlDebugConnection *client)
 
 void QmlToolsClient::messageReceived(const QByteArray &message)
 {
-    QPacket ds(connection()->currentDataStreamVersion(), message);
+    QPacket ds(dataStreamVersion(), message);
 
     QByteArray type;
     int requestId;
@@ -98,7 +98,7 @@ void QmlToolsClient::setObjectIdList(const QList<ObjectReference> &objectRoots)
     foreach (const ObjectReference &object, objectRoots)
         debugIds << object.debugId();
 
-    QPacket ds(connection()->currentDataStreamVersion());
+    QPacket ds(dataStreamVersion());
     ds << QByteArray(REQUEST) << m_requestId++ << QByteArray(SELECT) << debugIds;
     sendMessage(ds.data());
 }
@@ -108,7 +108,7 @@ void QmlToolsClient::setDesignModeBehavior(bool inDesignMode)
     if (!m_connection || !m_connection->isConnected())
         return;
 
-    QPacket ds(connection()->currentDataStreamVersion());
+    QPacket ds(dataStreamVersion());
     ds << QByteArray(REQUEST) << m_requestId++;
     if (inDesignMode)
         ds << QByteArray(ENABLE);
@@ -140,7 +140,7 @@ void QmlToolsClient::showAppOnTop(bool showOnTop)
     if (!m_connection || !m_connection->isConnected())
         return;
 
-    QPacket ds(connection()->currentDataStreamVersion());
+    QPacket ds(dataStreamVersion());
     ds << QByteArray(REQUEST) << m_requestId++
        << QByteArray(SHOW_APP_ON_TOP) << showOnTop;
 
diff --git a/src/plugins/debugger/qml/qmlengine.cpp b/src/plugins/debugger/qml/qmlengine.cpp
index 9ff977fc62e..f5f87fd3054 100644
--- a/src/plugins/debugger/qml/qmlengine.cpp
+++ b/src/plugins/debugger/qml/qmlengine.cpp
@@ -140,11 +140,10 @@ typedef QHash<int, LookupData> LookupItems; // id -> (iname, exp)
 class QmlEnginePrivate : public QmlDebugClient
 {
 public:
-    QmlEnginePrivate(QmlEngine *engine_, QmlDebugConnection *connection_)
-        : QmlDebugClient("V8Debugger", connection_),
+    QmlEnginePrivate(QmlEngine *engine_, QmlDebugConnection *connection)
+        : QmlDebugClient("V8Debugger", connection),
           engine(engine_),
-          inspectorAgent(engine, connection_),
-          connection(connection_)
+          inspectorAgent(engine, connection)
     {}
 
     void messageReceived(const QByteArray &data);
@@ -221,7 +220,6 @@ public:
     bool contextEvaluate = false;
 
     QTimer connectionTimer;
-    QmlDebug::QmlDebugConnection *connection;
     QmlDebug::QDebugMessageClient *msgClient = 0;
 
     QHash<int, QmlCallback> callbackForToken;
@@ -250,6 +248,7 @@ QmlEngine::QmlEngine(bool useTerminal)
   :  d(new QmlEnginePrivate(this, new QmlDebugConnection(this)))
 {
     setObjectName("QmlEngine");
+    QmlDebugConnection *connection = d->connection();
 
     connect(stackHandler(), &StackHandler::stackChanged,
             this, &QmlEngine::updateCurrentContext);
@@ -280,21 +279,21 @@ QmlEngine::QmlEngine(bool useTerminal)
     connect(&d->connectionTimer, &QTimer::timeout,
             this, &QmlEngine::checkConnectionState);
 
-    connect(d->connection, &QmlDebugConnection::logStateChange,
+    connect(connection, &QmlDebugConnection::logStateChange,
             this, &QmlEngine::showConnectionStateMessage);
-    connect(d->connection, &QmlDebugConnection::logError, this,
+    connect(connection, &QmlDebugConnection::logError, this,
             [this](const QString &error) { showMessage("QML Debugger: " + error, LogWarning); });
 
-    connect(d->connection, &QmlDebugConnection::connectionFailed,
+    connect(connection, &QmlDebugConnection::connectionFailed,
             this, &QmlEngine::connectionFailed);
-    connect(d->connection, &QmlDebugConnection::connected,
+    connect(connection, &QmlDebugConnection::connected,
             &d->connectionTimer, &QTimer::stop);
-    connect(d->connection, &QmlDebugConnection::connected,
+    connect(connection, &QmlDebugConnection::connected,
             this, &QmlEngine::connectionEstablished);
-    connect(d->connection, &QmlDebugConnection::disconnected,
+    connect(connection, &QmlDebugConnection::disconnected,
             this, &QmlEngine::disconnected);
 
-    d->msgClient = new QDebugMessageClient(d->connection);
+    d->msgClient = new QDebugMessageClient(connection);
     connect(d->msgClient, &QDebugMessageClient::newState,
             this, [this](QmlDebugClient::State state) {
         logServiceStateChange(d->msgClient->name(), d->msgClient->serviceVersion(), state);
@@ -404,10 +403,11 @@ void QmlEngine::beginConnection()
      */
     int port = runParameters().qmlServer.port();
 
-    if (!d->connection || d->connection->isConnected())
+    QmlDebugConnection *connection = d->connection();
+    if (!connection || connection->isConnected())
         return;
 
-    d->connection->connectToHost(host, port);
+    connection->connectToHost(host, port);
 
     //A timeout to check the connection state
     d->connectionTimer.start();
@@ -513,8 +513,8 @@ void QmlEngine::closeConnection()
     if (d->connectionTimer.isActive()) {
         d->connectionTimer.stop();
     } else {
-        if (d->connection)
-            d->connection->close();
+        if (QmlDebugConnection *connection = d->connection())
+            connection->close();
     }
 }
 
@@ -1194,7 +1194,10 @@ void QmlEngine::checkConnectionState()
 
 bool QmlEngine::isConnected() const
 {
-    return d->connection->isConnected();
+    if (QmlDebugConnection *connection = d->connection())
+        return connection->isConnected();
+    else
+        return false;
 }
 
 void QmlEngine::showConnectionStateMessage(const QString &message)
@@ -1452,7 +1455,7 @@ void QmlEnginePrivate::setBreakpoint(const QString type, const QString target,
     //                    }
     //    }
     if (type == EVENT) {
-        QPacket rs(connection->currentDataStreamVersion());
+        QPacket rs(dataStreamVersion());
         rs <<  target.toUtf8() << enabled;
         engine->showMessage(QString("%1 %2 %3")
                             .arg(BREAKONSIGNAL, target, QLatin1String(enabled ? "enabled" : "disabled")), LogInput);
@@ -1672,7 +1675,7 @@ void QmlEnginePrivate::runDirectCommand(const QString &type, const QByteArray &m
 
     engine->showMessage(QString("%1 %2").arg(type, QString::fromLatin1(msg)), LogInput);
 
-    QPacket rs(connection->currentDataStreamVersion());
+    QPacket rs(dataStreamVersion());
     rs << cmd << type.toLatin1() << msg;
 
     if (state() == Enabled)
@@ -1694,7 +1697,7 @@ void QmlEnginePrivate::memorizeRefs(const QVariant &refs)
 
 void QmlEnginePrivate::messageReceived(const QByteArray &data)
 {
-    QPacket ds(connection->currentDataStreamVersion(), data);
+    QPacket ds(dataStreamVersion(), data);
     QByteArray command;
     ds >> command;
 
diff --git a/src/plugins/qmlprofiler/qmlprofilertraceclient.cpp b/src/plugins/qmlprofiler/qmlprofilertraceclient.cpp
index 76dbf370097..a48123a9a40 100644
--- a/src/plugins/qmlprofiler/qmlprofilertraceclient.cpp
+++ b/src/plugins/qmlprofiler/qmlprofilertraceclient.cpp
@@ -166,7 +166,7 @@ void QmlProfilerTraceClientPrivate::processCurrentEvent()
 
 void QmlProfilerTraceClientPrivate::sendRecordingStatus(int engineId)
 {
-    QmlDebug::QPacket stream(q->connection()->currentDataStreamVersion());
+    QmlDebug::QPacket stream(q->dataStreamVersion());
     stream << recording << engineId; // engineId -1 is OK. It means "all of them"
     if (recording) {
         stream << requestedFeatures << flushInterval;
@@ -282,7 +282,7 @@ void QmlProfilerTraceClient::stateChanged(State status)
 
 void QmlProfilerTraceClient::messageReceived(const QByteArray &data)
 {
-    QmlDebug::QPacket stream(connection()->currentDataStreamVersion(), data);
+    QmlDebug::QPacket stream(dataStreamVersion(), data);
 
     stream >> d->currentEvent;