--- src/events.c
+++ src/events.c	2012-05-31 15:13:06.832009873 +0000
@@ -1611,8 +1611,11 @@ upshift_event (Lisp_Object event)
     XSET_EVENT_KEY_KEYSYM (event, make_char (c + 'A' - 'a'));
   else
     if (!(XEVENT_KEY_MODIFIERS (event) & XEMACS_MOD_SHIFT))
-      XSET_EVENT_KEY_MODIFIERS
-	(event, XEVENT_KEY_MODIFIERS (event) |= XEMACS_MOD_SHIFT);
+      {
+	Lisp_Object tmp = XEVENT_KEY_MODIFIERS (event);
+	tmp |= XEMACS_MOD_SHIFT;
+	XSET_EVENT_KEY_MODIFIERS (event, tmp);
+      }
 }
 
 void