diff -up tk8.5.3/generic/tkEvent.c.crash1 tk8.5.3/generic/tkEvent.c
--- tk8.5.3/generic/tkEvent.c.crash1	2008-03-26 20:04:09.000000000 +0100
+++ tk8.5.3/generic/tkEvent.c	2008-08-06 09:47:03.000000000 +0200
@@ -75,7 +75,7 @@ typedef struct TkWindowEvent {
  * Array of event masks corresponding to each X event:
  */
 
-static unsigned long eventMasks[TK_LASTEVENT] = {
+static unsigned long realEventMasks[MappingNotify+1] = {
     0,
     0,
     KeyPressMask,			/* KeyPress */
@@ -113,7 +113,10 @@ static unsigned long eventMasks[TK_LASTE
     0,					/* SelectionNotify */
     ColormapChangeMask,			/* ColormapNotify */
     0,					/* ClientMessage */
-    0,					/* Mapping Notify */
+    0					/* Mapping Notify */
+};
+
+static unsigned long virtualEventMasks[TK_LASTEVENT-VirtualEvent] = {
     VirtualEventMask,			/* VirtualEvents */
     ActivateMask,			/* ActivateNotify */
     ActivateMask,			/* DeactivateNotify */
@@ -489,7 +492,7 @@ GetTkWindowFromXEvent(
  *
  * GetEventMaskFromXEvent --
  *
- *	The event type is looked up in our eventMasks table, and may be
+ *	The event type is looked up in our eventMasks tables, and may be
  *	changed to a different mask depending on the state of the event and
  *	window members.
  *
@@ -506,7 +509,23 @@ static unsigned long
 GetEventMaskFromXEvent(
     XEvent *eventPtr)
 {
-    unsigned long mask = eventMasks[eventPtr->xany.type];
+    unsigned long mask;
+
+    /*
+     * Get the event mask from the correct table. Note that there are two
+     * tables here because that means we no longer need this code to rely on
+     * the exact value of VirtualEvent, which has caused us problems in the
+     * past when X11 changed the value of LASTEvent. [Bug ???]
+     */
+
+    if (eventPtr->xany.type <= MappingNotify) {
+	    mask = realEventMasks[eventPtr->xany.type];
+    } else if (eventPtr->xany.type >= VirtualEvent
+	    && eventPtr->xany.type<TK_LASTEVENT) {
+	    mask = virtualEventMasks[eventPtr->xany.type - VirtualEvent]; 
+    } else {
+        mask = 0;
+    }
 
     /*
      * Events selected by StructureNotify require special handling. They look
diff -up tk8.5.3/generic/tk.h.crash1 tk8.5.3/generic/tk.h
--- tk8.5.3/generic/tk.h.crash1	2008-06-30 05:37:37.000000000 +0200
+++ tk8.5.3/generic/tk.h	2008-08-06 09:47:40.000000000 +0200
@@ -627,17 +627,15 @@ typedef struct Tk_GeomMgr {
  *---------------------------------------------------------------------------
  */
 
-#define VirtualEvent	    (LASTEvent)
-#define ActivateNotify	    (LASTEvent + 1)
-#define DeactivateNotify    (LASTEvent + 2)
-#define MouseWheelEvent     (LASTEvent + 3)
-#define TK_LASTEVENT	    (LASTEvent + 4)
+#define VirtualEvent	    (MappingNotify + 1)
+#define ActivateNotify	    (MappingNotify + 2)
+#define DeactivateNotify    (MappingNotify + 3)
+#define MouseWheelEvent     (MappingNotify + 4)
+#define TK_LASTEVENT	    (MappingNotify + 5)
 
 #define MouseWheelMask	    (1L << 28)
-
 #define ActivateMask	    (1L << 29)
 #define VirtualEventMask    (1L << 30)
-#define TK_LASTEVENT	    (LASTEvent + 4)
 
 /*
  * A virtual event shares most of its fields with the XKeyEvent and