diff --git a/src/plugins/debugger/debuggerrunner.cpp b/src/plugins/debugger/debuggerrunner.cpp
index 89d4437a2e3fc8ca12272a74d857635781e57cbd..cf83be4186dc1af8bc9311d8d5e884b771061670 100644
--- a/src/plugins/debugger/debuggerrunner.cpp
+++ b/src/plugins/debugger/debuggerrunner.cpp
@@ -745,8 +745,8 @@ static DebuggerStartParameters localStartParameters(RunConfiguration *runConfigu
             sp.environment.set(optimizerKey, _("1"));
         }
 
-        Utils::QtcProcess::addArg(&sp.processArgs, _("-qmljsdebugger=port:")
-                                  + QString::number(sp.qmlServerPort));
+        Utils::QtcProcess::addArg(&sp.processArgs, QString("-qmljsdebugger=port:%1,block").arg(
+                                      sp.qmlServerPort));
     }
 
     // FIXME: If it's not yet build this will be empty and not filled
diff --git a/src/plugins/qmlprojectmanager/qmlprojectruncontrol.cpp b/src/plugins/qmlprojectmanager/qmlprojectruncontrol.cpp
index 0685af95b6d09142288b2f37da192f725fbaad0c..07e31679f056b07d634aca0887ac661e00d7caf8 100644
--- a/src/plugins/qmlprojectmanager/qmlprojectruncontrol.cpp
+++ b/src/plugins/qmlprojectmanager/qmlprojectruncontrol.cpp
@@ -202,7 +202,7 @@ RunControl *QmlProjectRunControlFactory::createDebugRunControl(QmlProjectRunConf
     params.executable = runConfig->observerPath();
     params.qmlServerAddress = "127.0.0.1";
     params.qmlServerPort = runConfig->qmlDebugServerPort();
-    params.processArgs = QLatin1String("-qmljsdebugger=port:") + QString::number(runConfig->qmlDebugServerPort());
+    params.processArgs = QString("-qmljsdebugger=port:%1,block").arg(runConfig->qmlDebugServerPort());
     params.processArgs += QLatin1Char(' ') + runConfig->viewerArguments();
     params.workingDirectory = runConfig->workingDirectory();
     params.environment = runConfig->environment();
diff --git a/src/plugins/qt4projectmanager/qt-s60/s60devicerunconfiguration.cpp b/src/plugins/qt4projectmanager/qt-s60/s60devicerunconfiguration.cpp
index ee61aaee7f82291a7ab54b8cdc239029d9adfa2f..0f36a536632be71a8e647749d1b0de63ad2c3727 100644
--- a/src/plugins/qt4projectmanager/qt-s60/s60devicerunconfiguration.cpp
+++ b/src/plugins/qt4projectmanager/qt-s60/s60devicerunconfiguration.cpp
@@ -313,7 +313,7 @@ QString S60DeviceRunConfiguration::qmlCommandLineArguments() const
         QTC_ASSERT(activeDeployConf, return args);
 
         if (activeDeployConf->communicationChannel() == S60DeployConfiguration::CommunicationCodaTcpConnection)
-            args = QString("-qmljsdebugger=port:%1").arg(qmlDebugServerPort());
+            args = QString("-qmljsdebugger=port:%1,block").arg(qmlDebugServerPort());
         else
             args = QString("-qmljsdebugger=ost");
     }