diff --git a/src/backend/optimizer/plan/planner.c b/src/backend/optimizer/plan/planner.c
index 6770836..5c5e5ab 100644
--- a/src/backend/optimizer/plan/planner.c
+++ b/src/backend/optimizer/plan/planner.c
@@ -4305,7 +4305,10 @@ make_partialgroup_input_target(PlannerInfo *root, PathTarget *final_target)
 	foreach(lc, final_target->exprs)
 	{
 		Expr	   *expr = (Expr *) lfirst(lc);
-		Index		sgref = final_target->sortgrouprefs[i];
+		Index		sgref = 0;
+
+		if (final_target->sortgrouprefs != NULL)
+			sgref = final_target->sortgrouprefs[i];
 
 		if (sgref && parse->groupClause &&
 			get_sortgroupref_clause_noerr(sgref, parse->groupClause) != NULL)