diff --git a/effects.cpp b/effects.cpp
index 889cd35d4e..b124ee4146 100644
--- a/effects.cpp
+++ b/effects.cpp
@@ -1340,6 +1340,12 @@ QRect EffectWindowImpl::contentsRect() const
     return QRect( toplevel->clientPos(), toplevel->clientSize());
     }
 
+QRect EffectWindowImpl::decorationInnerRect() const
+    {
+    Client *client = dynamic_cast<Client*>(toplevel);
+    return client ? client->transparentRect() : contentsRect();
+    }
+
 QByteArray EffectWindowImpl::readProperty( long atom, long type, int format ) const
     {
     return readWindowProperty( window()->window(), atom, type, format );
diff --git a/effects.h b/effects.h
index 8aef7a426c..873b7620d5 100644
--- a/effects.h
+++ b/effects.h
@@ -239,6 +239,7 @@ class EffectWindowImpl : public EffectWindow
         virtual bool isUserResize() const;
         virtual QRect iconGeometry() const;
         virtual QRect contentsRect() const;
+        virtual QRect decorationInnerRect() const;
         virtual QByteArray readProperty( long atom, long type, int format ) const;
         virtual void deleteProperty( long atom ) const;
 
diff --git a/lib/kwineffects.h b/lib/kwineffects.h
index a2fc14a111..3270fe5969 100644
--- a/lib/kwineffects.h
+++ b/lib/kwineffects.h
@@ -864,6 +864,12 @@ class KWIN_EXPORT EffectWindow
          * Geometry of the actual window contents inside the whole (including decorations) window.
          */
         virtual QRect contentsRect() const = 0;
+        /**
+         * Geometry of the transparent rect in the decoration.
+         * May be different from contentsRect() if the decoration is extended into the client area.
+         * @since 4.5
+         */
+        virtual QRect decorationInnerRect() const = 0;
         bool hasDecoration() const;
         virtual QByteArray readProperty( long atom, long type, int format ) const = 0;
         virtual void deleteProperty( long atom ) const = 0;