diff -r 8d9fb810462b -r 7ef8d77ee761 src/Pure/GUI/gui.scala
--- a/src/Pure/GUI/gui.scala	Tue Jan 05 20:53:57 2021 +0100
+++ b/src/Pure/GUI/gui.scala	Tue Jan 05 21:46:35 2021 +0100
@@ -157,6 +157,21 @@
 
   def isabelle_image(): Image = isabelle_icon().getImage
 
+  def isabelle_image_large(): Image =
+    Toolkit.getDefaultToolkit.getImage(
+      File.platform_path(Path.explode("~~/lib/logo/isabelle_transparent-128.png")))
+
+  def set_application_icon()
+  {
+    if (Platform.is_macos) {
+      val image = isabelle_image_large()
+      val app =
+        Class.forName("com.apple.eawt.Application")
+          .getDeclaredMethod("getApplication").invoke(null)
+      app.getClass.getDeclaredMethod("setDockIconImage", classOf[Image]).invoke(app, image)
+    }
+  }
+
 
   /* location within multi-screen environment */