diff --git a/abstract_client.h b/abstract_client.h
--- a/abstract_client.h
+++ b/abstract_client.h
@@ -425,8 +425,7 @@
     virtual bool isHiddenInternal() const = 0;
     // TODO: remove boolean trap
     virtual void hideClient(bool hide) = 0;
-    bool isFullScreenable() const;
-    bool isFullScreenable(bool fullscreen_hack) const;
+    virtual bool isFullScreenable() const = 0;
     virtual bool isFullScreen() const = 0;
     // TODO: remove boolean trap
     virtual AbstractClient *findModal(bool allow_itself = false) = 0;
diff --git a/client.h b/client.h
--- a/client.h
+++ b/client.h
@@ -143,6 +143,7 @@
     bool isMinimizable() const override;
     QRect iconGeometry() const override;
 
+    bool isFullScreenable() const override;
     void setFullScreen(bool set, bool user = true) override;
     bool isFullScreen() const override;
     bool userCanSetFullScreen() const override;
@@ -347,6 +348,8 @@
 
     Client* findAutogroupCandidate() const;
 
+    bool isFullScreenable(bool fullscreenHack) const;
+
 protected:
     virtual void debug(QDebug& stream) const;
     void addDamage(const QRegion &damage) override;
diff --git a/client.cpp b/client.cpp
--- a/client.cpp
+++ b/client.cpp
@@ -595,6 +595,30 @@
     return noborder;
 }
 
+bool Client::isFullScreenable() const
+{
+    return isFullScreenable(false);
+}
+
+bool Client::isFullScreenable(bool fullscreenHack) const
+{
+    if (!rules()->checkFullScreen(true)) {
+        return false;
+    }
+    if (fullscreenHack) {
+        return isNormalWindow();
+    }
+    if (rules()->checkStrictGeometry(true)) {
+        // check geometry constraints (rule to obey is set)
+        const QRect fsarea = workspace()->clientArea(FullScreenArea, this);
+        if (sizeForClientSize(fsarea.size(), SizemodeAny, true) != fsarea.size()) {
+            return false; // the app wouldn't fit exactly fullscreen geometry due to its strict geometry requirements
+        }
+    }
+    // don't check size constrains - some apps request fullscreen despite requesting fixed size
+    return !isSpecialWindow(); // also better disallow only weird types to go fullscreen
+}
+
 bool Client::noBorder() const
 {
     return userNoBorder() || isFullScreen();
diff --git a/geometry.cpp b/geometry.cpp
--- a/geometry.cpp
+++ b/geometry.cpp
@@ -2449,26 +2449,6 @@
     emit quickTileModeChanged();
 }
 
-bool AbstractClient::isFullScreenable() const
-{
-    return isFullScreenable(false);
-}
-
-bool AbstractClient::isFullScreenable(bool fullscreen_hack) const
-{
-    if (!rules()->checkFullScreen(true))
-        return false;
-    if (fullscreen_hack)
-        return isNormalWindow();
-    if (rules()->checkStrictGeometry(true)) { // allow rule to ignore geometry constraints
-        QRect fsarea = workspace()->clientArea(FullScreenArea, this);
-        if (sizeForClientSize(fsarea.size(), SizemodeAny, true) != fsarea.size())
-            return false; // the app wouldn't fit exactly fullscreen geometry due to its strict geometry requirements
-    }
-    // don't check size constrains - some apps request fullscreen despite requesting fixed size
-    return !isSpecialWindow(); // also better disallow only weird types to go fullscreen
-}
-
 bool Client::userCanSetFullScreen() const
 {
     if (fullscreen_mode == FullScreenHack)
diff --git a/shell_client.h b/shell_client.h
--- a/shell_client.h
+++ b/shell_client.h
@@ -77,6 +77,7 @@
     void closeWindow() override;
     AbstractClient *findModal(bool allow_itself = false) override;
     bool isCloseable() const override;
+    bool isFullScreenable() const override;
     bool isFullScreen() const override;
     bool isMaximizable() const override;
     bool isMinimizable() const override;
diff --git a/shell_client.cpp b/shell_client.cpp
--- a/shell_client.cpp
+++ b/shell_client.cpp
@@ -931,6 +931,14 @@
     return true;
 }
 
+bool ShellClient::isFullScreenable() const
+{
+    if (!rules()->checkFullScreen(true)) {
+        return false;
+    }
+    return !isSpecialWindow();
+}
+
 void ShellClient::setFullScreen(bool set, bool user)
 {
     if (!isFullScreen() && !set)