*** a/src/backend/parser/parse_expr.c
--- b/src/backend/parser/parse_expr.c
***************
*** 1068,1074 **** transformAExprNullIf(ParseState *pstate, A_Expr *a)
  	if (result->opretset)
  		ereport(ERROR,
  				(errcode(ERRCODE_DATATYPE_MISMATCH),
! 				 errmsg("NULLIF operator must not return a set"),
  				 parser_errposition(pstate, a->location)));
  
  	/*
--- 1068,1075 ----
  	if (result->opretset)
  		ereport(ERROR,
  				(errcode(ERRCODE_DATATYPE_MISMATCH),
! 		/* translator: %s is name of a SQL construct, eg NULLIF */
! 				 errmsg("%s operator must not return a set", "NULLIF"),
  				 parser_errposition(pstate, a->location)));
  
  	/*
***************
*** 3041,3047 **** make_distinct_op(ParseState *pstate, List *opname, Node *ltree, Node *rtree,
  	if (((OpExpr *) result)->opretset)
  		ereport(ERROR,
  				(errcode(ERRCODE_DATATYPE_MISMATCH),
! 				 errmsg("IS DISTINCT FROM operator must not return a set"),
  				 parser_errposition(pstate, location)));
  
  	/*
--- 3042,3050 ----
  	if (((OpExpr *) result)->opretset)
  		ereport(ERROR,
  				(errcode(ERRCODE_DATATYPE_MISMATCH),
! 		/* translator: %s is name of a SQL construct, eg NULLIF */
! 				 errmsg("%s operator must not return a set",
! 						"IS DISTINCT FROM"),
  				 parser_errposition(pstate, location)));
  
  	/*