diff --git a/src/backend/optimizer/prep/prepagg.c b/src/backend/optimizer/prep/prepagg.c
index 89046f9afb..b688ff54e5 100644
--- a/src/backend/optimizer/prep/prepagg.c
+++ b/src/backend/optimizer/prep/prepagg.c
@@ -515,8 +515,8 @@ GetAggInitVal(Datum textInitVal, Oid transtype)
 
 /*
  * get_agg_clause_costs
- *	  Recursively find the Aggref nodes in an expression tree, and
- *	  accumulate cost information about them.
+ *	  Process the PlannerInfo's aggtransinfos and agginfos calculating the
+ *	  cost information about them.
  *
  * 'aggsplit' tells us the expected partial-aggregation mode, which affects
  * the cost estimates.
@@ -533,10 +533,6 @@ GetAggInitVal(Datum textInitVal, Oid transtype)
  * In addition, we mark Aggref nodes with the correct aggtranstype, so
  * that that doesn't need to be done repeatedly.  (That makes this function's
  * name a bit of a misnomer.)
- *
- * This does not descend into subqueries, and so should be used only after
- * reduction of sublinks to subplans, or in contexts where it's known there
- * are no subqueries.  There mustn't be outer-aggregate references either.
  */
 void
 get_agg_clause_costs(PlannerInfo *root, AggSplit aggsplit, AggClauseCosts *costs)