diff --git a/mozilla/js/src/jsemit.c b/mozilla/js/src/jsemit.c
index 6adf392aa66..7a1c30773b8 100644
--- a/mozilla/js/src/jsemit.c
+++ b/mozilla/js/src/jsemit.c
@@ -1831,6 +1831,10 @@ EmitAtomOp(JSContext *cx, JSParseNode *pn, JSOp op, JSCodeGenerator *cg)
  * or not pn->pn_op was modified, if this function finds an argument or local
  * variable name, pn->pn_attrs will contain the property's attributes after a
  * successful return.
+ *
+ * NB: if you add more opcodes specialized from JSOP_NAME, etc., don't forget
+ * to update the TOK_FOR (for-in) and TOK_ASSIGN (op=, e.g. +=) special cases
+ * in js_EmitTree.
  */
 static JSBool
 BindNameToSlot(JSContext *cx, JSTreeContext *tc, JSParseNode *pn)