diff --git a/src/apprt/gtk/class/window.zig b/src/apprt/gtk/class/window.zig
index 2a1a5435a2b..61a4adf09c9 100644
--- a/src/apprt/gtk/class/window.zig
+++ b/src/apprt/gtk/class/window.zig
@@ -1156,6 +1156,27 @@ pub const Window = extern struct {
         };
     }
 
+    fn toplevelComputeSize(
+        _: *gdk.Toplevel,
+        size: *gdk.ToplevelSize,
+        self: *Self,
+    ) callconv(.c) void {
+        // GTK clamps the requested size to stale monitor bounds. Re-assert the
+        // current surface size so an interactive resize isn't clamped. Skip the
+        // initial map (size still 0), and cases the compositor/quick terminal
+        // own (maximized, fullscreen, quick terminal).
+        if (self.isMaximized() or
+            self.isFullscreen() or
+            self.isQuickTerminal()) return;
+
+        const gdk_surface = self.as(gtk.Native).getSurface() orelse return;
+        const w = gdk_surface.getWidth();
+        const h = gdk_surface.getHeight();
+        if (w <= 0 or h <= 0) return;
+
+        size.setSize(w, h);
+    }
+
     fn propFullscreened(
         _: *adw.ApplicationWindow,
         _: *gobject.ParamSpec,
@@ -1330,6 +1351,16 @@ pub const Window = extern struct {
                 self,
                 .{ .detail = "height" },
             );
+            // Connect after GTK's compute-size handler so our size wins.
+            if (gobject.ext.cast(gdk.Toplevel, gdk_surface)) |toplevel| {
+                _ = gdk.Toplevel.signals.compute_size.connect(
+                    toplevel,
+                    *Self,
+                    toplevelComputeSize,
+                    self,
+                    .{ .after = true },
+                );
+            }
         }
 
         // When we are realized we always setup our appearance since this