--- glyphs-x.c~	Mon Sep 20 13:14:47 1999
+++ glyphs-x.c	Tue Sep 21 09:25:46 1999
@@ -2217,6 +2217,14 @@
   else				/* must be a widget */
     {
       Arg al[2];
+
+      if (!XtIsRealized (IMAGE_INSTANCE_X_WIDGET_ID (ii)))
+	{
+	  Lisp_Object sw;
+	  XSETIMAGE_INSTANCE (sw, ii);
+	  signal_simple_error ("XEmacs bug: subwindow is not realized", sw);
+	}
+
       XtSetArg (al [0], XtNwidth, (Dimension)w);
       XtSetArg (al [1], XtNheight, (Dimension)h);
       XtSetValues (IMAGE_INSTANCE_X_WIDGET_ID (ii), al, 2);