diff --git a/src/netwm_def.h b/src/netwm_def.h
--- a/src/netwm_def.h
+++ b/src/netwm_def.h
@@ -710,6 +710,7 @@
         @li WM2IconPixmap icon pixmap and mask in WM_HINTS (see ICCCM 4.1.2.4)
         @li WM2OpaqueRegion
         @li WM2DesktopFileName the base name of the desktop file name or the full path to the desktop file
+        @li WM2GTKFrameExtents extents of the shadow drawn by the client
     **/
     enum Property2 {
         WM2UserTime            = 1u << 0,
@@ -740,6 +741,7 @@
         WM2IconPixmap          = 1u << 25, // @since 5.7
         WM2OpaqueRegion        = 1u << 25, // @since 5.7
         WM2DesktopFileName     = 1u << 26, // NOT STANDARD @since 5.28
+        WM2GTKFrameExtents     = 1u << 27, // NOT STANDARD @since 5.64
         WM2AllProperties       = ~0u
     };
     Q_DECLARE_FLAGS(Properties2, Property2)
diff --git a/src/platforms/xcb/atoms_p.h b/src/platforms/xcb/atoms_p.h
--- a/src/platforms/xcb/atoms_p.h
+++ b/src/platforms/xcb/atoms_p.h
@@ -160,6 +160,9 @@
     // deprecated and naming convention violation
     ENUM(_NET_WM_STATE_STAYS_ON_TOP),
 
+    // GTK extensions
+    ENUM(_GTK_FRAME_EXTENTS),
+
     // application protocols
     ENUM(WM_PROTOCOLS),
     ENUM(WM_TAKE_FOCUS),
diff --git a/src/platforms/xcb/netwm.h b/src/platforms/xcb/netwm.h
--- a/src/platforms/xcb/netwm.h
+++ b/src/platforms/xcb/netwm.h
@@ -1309,6 +1309,20 @@
     **/
     NETStrut frameOverlap() const;
 
+    /**
+       Sets the extents of the drop-shadow drawn by the client.
+
+       @since 5.64
+    **/
+    void setGtkFrameExtents(NETStrut strut);
+
+    /**
+       Returns the extents of the drop-shadow drawn by a GTK client.
+
+       @since 5.64
+    **/
+    NETStrut gtkFrameExtents() const;
+
     /**
        Returns an icon.  If width and height are passed, the icon returned will be
        the closest it can find (the next biggest).  If width and height are omitted,
diff --git a/src/platforms/xcb/netwm.cpp b/src/platforms/xcb/netwm.cpp
--- a/src/platforms/xcb/netwm.cpp
+++ b/src/platforms/xcb/netwm.cpp
@@ -1146,6 +1146,10 @@
         atoms[pnum++] = p->atom(_NET_WM_OPAQUE_REGION);
     }
 
+    if (p->properties2 & WM2GTKFrameExtents) {
+        atoms[pnum++] = p->atom(_GTK_FRAME_EXTENTS);
+    }
+
     xcb_change_property(p->conn, XCB_PROP_MODE_REPLACE, p->root, p->atom(_NET_SUPPORTED),
                         XCB_ATOM_ATOM, 32, pnum, (const void *) atoms);
 
@@ -1446,6 +1450,10 @@
     else if (atom == p->atom(_NET_WM_OPAQUE_REGION)) {
         p->properties2 |= WM2OpaqueRegion;
     }
+
+    else if (atom == p->atom(_GTK_FRAME_EXTENTS)) {
+        p->properties2 |= WM2GTKFrameExtents;
+    }
 }
 
 void NETRootInfo::setActiveWindow(xcb_window_t window)
@@ -3500,6 +3508,25 @@
     return p->frame_overlap;
 }
 
+void NETWinInfo::setGtkFrameExtents(NETStrut strut)
+{
+    p->gtk_frame_extents = strut;
+
+    uint32_t d[4];
+    d[0] = strut.left;
+    d[1] = strut.right;
+    d[2] = strut.top;
+    d[3] = strut.bottom;
+
+    xcb_change_property(p->conn, XCB_PROP_MODE_REPLACE, p->window, p->atom(_GTK_FRAME_EXTENTS),
+                        XCB_ATOM_CARDINAL, 32, 4, (const void *) d);
+}
+
+NETStrut NETWinInfo::gtkFrameExtents() const
+{
+    return p->gtk_frame_extents;
+}
+
 void NETWinInfo::kdeGeometry(NETRect &frame, NETRect &window)
 {
     if (p->win_geom.size.width == 0 || p->win_geom.size.height == 0) {
@@ -3818,6 +3845,8 @@
             dirty2 = WM2DesktopFileName;
         } else if (pe->atom == p->atom(_NET_WM_FULLSCREEN_MONITORS)) {
             dirty2 = WM2FullscreenMonitors;
+        } else if (pe->atom == p->atom(_GTK_FRAME_EXTENTS)) {
+            dirty2 |= WM2GTKFrameExtents;
         }
 
         do_update = true;
@@ -4009,6 +4038,10 @@
         cookies[c++] = xcb_get_property(p->conn, false, p->window, p->atom(_KDE_NET_WM_DESKTOP_FILE), p->atom(UTF8_STRING), 0, MAX_PROP_SIZE);
     }
 
+    if (dirty2 & WM2GTKFrameExtents) {
+        cookies[c++] = xcb_get_property(p->conn, false, p->window, p->atom(_GTK_FRAME_EXTENTS), XCB_ATOM_CARDINAL, 0, 4);
+    }
+
     c = 0;
 
     if (dirty & XAWMState) {
@@ -4594,6 +4627,18 @@
             p->desktop_file = nstrndup(id.constData(), id.length());
         }
     }
+
+    if (dirty2 & WM2GTKFrameExtents) {
+        p->gtk_frame_extents = NETStrut();
+
+        QVector<uint32_t> data = get_array_reply<uint32_t>(p->conn, cookies[c++], XCB_ATOM_CARDINAL);
+        if (data.count() == 4) {
+            p->gtk_frame_extents.left   = data[0];
+            p->gtk_frame_extents.right  = data[1];
+            p->gtk_frame_extents.top    = data[2];
+            p->gtk_frame_extents.bottom = data[3];
+        }
+    }
 }
 
 NETRect NETWinInfo::iconGeometry() const
diff --git a/src/platforms/xcb/netwm_p.h b/src/platforms/xcb/netwm_p.h
--- a/src/platforms/xcb/netwm_p.h
+++ b/src/platforms/xcb/netwm_p.h
@@ -171,6 +171,7 @@
     NETStrut strut;
     NETStrut frame_strut; // strut?
     NETStrut frame_overlap;
+    NETStrut gtk_frame_extents;
     NETRArray<NET::WindowType> types;
     char *name, *visible_name, *icon_name, *visible_icon_name;
     int desktop;