diff --git a/src/substrait/textplan/PlanPrinterVisitor.cpp b/src/substrait/textplan/PlanPrinterVisitor.cpp
index 555ae28b..f2b12206 100644
--- a/src/substrait/textplan/PlanPrinterVisitor.cpp
+++ b/src/substrait/textplan/PlanPrinterVisitor.cpp
@@ -72,6 +72,7 @@ std::string visitEnumArgument(const std::string& str) {
 }
 
 bool isAggregate(const SymbolInfo* symbol) {
+  // TODO: Remove after the relation type is one type internally.
   if (const auto typeCase =
           ANY_CAST_IF(::substrait::proto::Rel::RelTypeCase, symbol->subtype)) {
     return (typeCase == ::substrait::proto::Rel::kAggregate);
diff --git a/src/substrait/textplan/parser/SubstraitPlanRelationVisitor.cpp b/src/substrait/textplan/parser/SubstraitPlanRelationVisitor.cpp
index 6bdeeab9..8b3dc157 100644
--- a/src/substrait/textplan/parser/SubstraitPlanRelationVisitor.cpp
+++ b/src/substrait/textplan/parser/SubstraitPlanRelationVisitor.cpp
@@ -317,6 +317,7 @@ bool isRelationEmitDetail(SubstraitPlanParser::Relation_detailContext* ctx) {
 }
 
 bool isAggregate(const SymbolInfo* symbol) {
+  // TODO: Remove once relation types have a unified type internally.
   if (const auto typeCase = ANY_CAST_IF(RelationType, symbol->subtype)) {
     return (typeCase == RelationType::kAggregate);
   }
diff --git a/src/substrait/textplan/parser/SubstraitPlanSubqueryRelationVisitor.cpp b/src/substrait/textplan/parser/SubstraitPlanSubqueryRelationVisitor.cpp
index 80812f75..c9a5f8c2 100644
--- a/src/substrait/textplan/parser/SubstraitPlanSubqueryRelationVisitor.cpp
+++ b/src/substrait/textplan/parser/SubstraitPlanSubqueryRelationVisitor.cpp
@@ -373,6 +373,7 @@ comparisonToProto(const std::string& text) {
 }
 
 bool isAggregate(const SymbolInfo* symbol) {
+  // TODO: Remove after the relation type is one type internally.
   if (const auto typeCase = ANY_CAST_IF(RelationType, symbol->subtype)) {
     return (typeCase == RelationType::kAggregate);
   }