diff --git a/src/abstract_client.cpp b/src/abstract_client.cpp
index 628c0315c0..8dae042ed8 100644
--- a/src/abstract_client.cpp
+++ b/src/abstract_client.cpp
@@ -9,6 +9,9 @@
 */
 #include "abstract_client.h"
 
+#ifdef KWIN_BUILD_ACTIVITIES
+#include "activities.h"
+#endif
 #include "appmenu.h"
 #include "decorations/decoratedclient.h"
 #include "decorations/decorationpalette.h"
@@ -2794,6 +2797,41 @@ void AbstractClient::setOnActivities(const QStringList &newActivitiesList)
     Q_UNUSED(newActivitiesList)
 }
 
+/**
+ * Sets whether the client is on @p activity.
+ * If you remove it from its last activity, then it's on all activities.
+ *
+ * Note: If it was on all activities and you try to remove it from one, nothing will happen;
+ * I don't think that's an important enough use case to handle here.
+ */
+void AbstractClient::setOnActivity(const QString &activity, bool enable)
+{
+#ifdef KWIN_BUILD_ACTIVITIES
+    if (!Activities::self()) {
+        return;
+    }
+    QStringList newActivitiesList = activities();
+    if (newActivitiesList.contains(activity) == enable) {
+        //nothing to do
+        return;
+    }
+    if (enable) {
+        QStringList allActivities = Activities::self()->all();
+        if (!allActivities.contains(activity)) {
+            //bogus ID
+            return;
+        }
+        newActivitiesList.append(activity);
+    } else {
+        newActivitiesList.removeOne(activity);
+    }
+    setOnActivities(newActivitiesList);
+#else
+    Q_UNUSED(activity)
+    Q_UNUSED(enable)
+#endif
+}
+
 void AbstractClient::checkNoBorder()
 {
     setNoBorder(false);
diff --git a/src/abstract_client.h b/src/abstract_client.h
index f3dd378e49..8797f00eea 100644
--- a/src/abstract_client.h
+++ b/src/abstract_client.h
@@ -539,6 +539,7 @@ public:
     virtual void checkNoBorder();
     virtual void setOnActivities(const QStringList &newActivitiesList);
     virtual void setOnAllActivities(bool set) = 0;
+    void setOnActivity(const QString &activity, bool enable);
     const WindowRules* rules() const {
         return &m_rules;
     }
diff --git a/src/x11client.cpp b/src/x11client.cpp
index 3a78d1ef1c..f714540d69 100644
--- a/src/x11client.cpp
+++ b/src/x11client.cpp
@@ -1878,36 +1878,6 @@ void X11Client::doSetDemandsAttention()
     info->setState(isDemandingAttention() ? NET::DemandsAttention : NET::States(), NET::DemandsAttention);
 }
 
-/**
- * Sets whether the client is on @p activity.
- * If you remove it from its last activity, then it's on all activities.
- *
- * Note: If it was on all activities and you try to remove it from one, nothing will happen;
- * I don't think that's an important enough use case to handle here.
- */
-void X11Client::setOnActivity(const QString &activity, bool enable)
-{
-#ifdef KWIN_BUILD_ACTIVITIES
-    if (! Activities::self()) {
-        return;
-    }
-    QStringList newActivitiesList = activities();
-    if (newActivitiesList.contains(activity) == enable)   //nothing to do
-        return;
-    if (enable) {
-        QStringList allActivities = Activities::self()->all();
-        if (!allActivities.contains(activity))   //bogus ID
-            return;
-        newActivitiesList.append(activity);
-    } else
-        newActivitiesList.removeOne(activity);
-    setOnActivities(newActivitiesList);
-#else
-    Q_UNUSED(activity)
-    Q_UNUSED(enable)
-#endif
-}
-
 /**
  * set exactly which activities this client is on
  */
diff --git a/src/x11client.h b/src/x11client.h
index dfca76d4a2..30631bf195 100644
--- a/src/x11client.h
+++ b/src/x11client.h
@@ -122,7 +122,6 @@ public:
     void destroyClient() override;
 
     QStringList activities() const override;
-    void setOnActivity(const QString &activity, bool enable);
     void setOnAllActivities(bool set) override;
     void setOnActivities(const QStringList &newActivitiesList) override;
     void updateActivities(bool includeTransients);