diff --git a/kcmkwin/kwinrules/ruleswidget.h b/kcmkwin/kwinrules/ruleswidget.h
--- a/kcmkwin/kwinrules/ruleswidget.h
+++ b/kcmkwin/kwinrules/ruleswidget.h
@@ -111,6 +111,7 @@
     QString comboToActivity(int val) const;
     void updateActivitiesList();
     KActivities::Consumer *m_activities;
+    QString m_selectedActivityId; // we need this for async activity loading
 #endif
     int comboToTiling(int val) const;
     int inc(int i) const { return i+1; }
diff --git a/kcmkwin/kwinrules/ruleswidget.cpp b/kcmkwin/kwinrules/ruleswidget.cpp
--- a/kcmkwin/kwinrules/ruleswidget.cpp
+++ b/kcmkwin/kwinrules/ruleswidget.cpp
@@ -298,6 +298,7 @@
         return NET::OnAllDesktops;
     return val + 1;
 }
+
 #ifdef KWIN_BUILD_ACTIVITIES
 int RulesWidget::activityToCombo(QString d) const
 {
@@ -335,8 +336,19 @@
             activity->addItem(info.name(), activityId);
         }
     }
+
+    auto rules = this->rules();
+    if (rules->activityrule == Rules::UnusedSetRule) {
+        enable_activity->setChecked(false);
+        Ui::RulesWidgetBase::activity->setCurrentIndex(0);
+    } else {
+        enable_activity->setChecked(true);
+        Ui::RulesWidgetBase::activity->setCurrentIndex(activityToCombo(m_selectedActivityId));
+    }
+    updateEnableactivity();
 }
 #endif
+
 static int placementToCombo(Placement::Policy placement)
 {
     static const int conv[] = {
@@ -472,6 +484,7 @@
     COMBOBOX_SET_RULE(desktop, desktopToCombo);
     SPINBOX_SET_RULE(screen, inc);
 #ifdef KWIN_BUILD_ACTIVITIES
+    m_selectedActivityId = rules->activity;
     COMBOBOX_SET_RULE(activity, activityToCombo);
 #endif
     CHECKBOX_SET_RULE(maximizehoriz,);