diff --git a/client.cpp b/client.cpp
index 5fb6dcb87c..e16a1fe7e4 100644
--- a/client.cpp
+++ b/client.cpp
@@ -1518,12 +1518,16 @@ void Client::setOnActivity(const QString &activity, bool enable)
 /**
  * set exactly which activities this client is on
  */
+#define NULL_UUID "00000000-0000-0000-0000-000000000000"
 void Client::setOnActivities(QStringList newActivitiesList)
 {
     QString joinedActivitiesList = newActivitiesList.join(",");
     joinedActivitiesList = rules()->checkActivity(joinedActivitiesList, false);
     newActivitiesList = joinedActivitiesList.split(',', QString::SkipEmptyParts);
 
+    if (newActivitiesList.contains(NULL_UUID))
+        newActivitiesList.clear(); // turn into "all"
+
     QStringList allActivities = workspace()->activityList();
     if ( newActivitiesList.isEmpty() ||
         (newActivitiesList.count() > 1 && newActivitiesList.count() == allActivities.count()) ||
@@ -2380,6 +2384,12 @@ void Client::checkActivities()
     }
 
     newActivitiesList = QString(prop).split(',');
+
+    if (newActivitiesList.contains(NULL_UUID)) {
+        setOnAllActivities(true);
+        return;
+    }
+
     if (newActivitiesList == activityList)
         return; //expected change, it's ok.