diff --git a/apps/opencs/model/tools/signalhandler.cpp b/apps/opencs/model/tools/signalhandler.cpp
index cfb52ed63..64e5ead55 100644
--- a/apps/opencs/model/tools/signalhandler.cpp
+++ b/apps/opencs/model/tools/signalhandler.cpp
@@ -1,5 +1,7 @@
 #include "signalhandler.hpp"
 
+#include <QMetaObject>
+
 #include "../settings/usersettings.hpp"
 
 CSMTools::SignalHandler::SignalHandler(bool extraCheck)
@@ -11,12 +13,20 @@ CSMTools::SignalHandler::SignalHandler(bool extraCheck)
              SLOT (updateUserSetting (const QString &, const QStringList &)));
 }
 
+// called from the main thread
 void CSMTools::SignalHandler::updateUserSetting (const QString &name, const QStringList &list)
 {
-    if (name=="verifier/pathgrid-extra-check")
-        mExtraCheck = list.at(0) == "true";
+    if (name=="verifier/pathgrid-extra-check" && !list.empty())
+        QMetaObject::invokeMethod(this, "updateExtraCheck", Qt::AutoConnection, Q_ARG(bool, list.at(0) == "true"));
 }
 
+// should be in the operations thread via an event message queue
+void CSMTools::SignalHandler::updateExtraCheck (bool extraCheck)
+{
+    mExtraCheck = extraCheck;
+}
+
+// called from the operations thread
 bool CSMTools::SignalHandler::extraCheck ()
 {
     return mExtraCheck;
diff --git a/apps/opencs/model/tools/signalhandler.hpp b/apps/opencs/model/tools/signalhandler.hpp
index c3d075fdf..bc063ebd6 100644
--- a/apps/opencs/model/tools/signalhandler.hpp
+++ b/apps/opencs/model/tools/signalhandler.hpp
@@ -20,6 +20,10 @@ namespace CSMTools
         public slots:
 
             void updateUserSetting (const QString &name, const QStringList &list);
+
+        private slots:
+
+            void updateExtraCheck (bool extraCheck);
     };
 }