src/java.desktop/unix/classes/sun/awt/X11/XDialogPeer.java

*** 57,66 ****
--- 57,69 ----
          winAttr.title = target.getTitle();
          winAttr.initialState = XWindowAttributesData.NORMAL;
      }
  
      public void setVisible(boolean vis) {
+         if (isDisposed()) {
+             return;
+         }
          XToolkit.awtLock();
          try {
              Dialog target = (Dialog)this.target;
              if (vis) {
                  if (target.getModalityType() != Dialog.ModalityType.MODELESS) {