diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 4c408404466..719545ed0c9 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -1953,7 +1953,8 @@ enum reflect_kind : addr_space_t {
 #define SPLICE_EXPR_EXPRESSION_P(NODE) \
    TREE_LANG_FLAG_0 (SPLICE_EXPR_CHECK (NODE))
 
-/* Helper macro to set SPLICE_EXPR_EXPRESSION_P.  */
+/* Helper macro to set SPLICE_EXPR_EXPRESSION_P.  This macro handles
+   dependent_splice_p trees: either [:T:] or [:T:]<arg>.  */
 #define SET_SPLICE_EXPR_EXPRESSION_P(NODE) \
   (SPLICE_EXPR_EXPRESSION_P (TREE_CODE (NODE) == SPLICE_EXPR \
 			     ? NODE : TREE_OPERAND (NODE, 0)) = true)