diff --git a/common/legacy_value.cc b/common/legacy_value.cc
index 622257f43..151d848af 100644
--- a/common/legacy_value.cc
+++ b/common/legacy_value.cc
@@ -1063,12 +1063,10 @@ absl::Status ModernValue(google::protobuf::Arena* arena,
       result = UnsafeTimestampValue(legacy_value.TimestampOrDie());
       return absl::OkStatus();
     case CelValue::Type::kList:
-      result =
-          ListValue(common_internal::LegacyListValue(legacy_value.ListOrDie()));
+      result = common_internal::FromLegacyList(legacy_value.ListOrDie());
       return absl::OkStatus();
     case CelValue::Type::kMap:
-      result =
-          MapValue(common_internal::LegacyMapValue(legacy_value.MapOrDie()));
+      result = common_internal::FromLegacyMap(legacy_value.MapOrDie());
       return absl::OkStatus();
     case CelValue::Type::kUnknownSet:
       result = common_internal::MakeUnknownValue(
@@ -1178,10 +1176,9 @@ absl::StatusOr<Value> FromLegacyValue(google::protobuf::Arena* arena,
     case CelValue::Type::kTimestamp:
       return UnsafeTimestampValue(legacy_value.TimestampOrDie());
     case CelValue::Type::kList:
-      return ListValue(
-          common_internal::LegacyListValue(legacy_value.ListOrDie()));
+      return common_internal::FromLegacyList(legacy_value.ListOrDie());
     case CelValue::Type::kMap:
-      return MapValue(common_internal::LegacyMapValue(legacy_value.MapOrDie()));
+      return common_internal::FromLegacyMap(legacy_value.MapOrDie());
     case CelValue::Type::kUnknownSet:
       return common_internal::MakeUnknownValue(*legacy_value.UnknownSetOrDie(),
                                                arena);
diff --git a/common/values/legacy_list_value.cc b/common/values/legacy_list_value.cc
index d3c1b94be..50bf1e6fe 100644
--- a/common/values/legacy_list_value.cc
+++ b/common/values/legacy_list_value.cc
@@ -80,6 +80,8 @@ class LegacyParsedRepeatedFieldListValue final
     return UnsafeLegacyValue(result, /*stable=*/false, arena);
   }
 
+  google::protobuf::Arena* absl_nonnull arena() const { return arena_; }
+
  protected:
   std::string DebugString() const override { return value_.DebugString(); }
 
@@ -202,6 +204,8 @@ class LegacyParsedJsonListValue final
     return UnsafeLegacyValue(result, /*stable=*/false, arena);
   }
 
+  google::protobuf::Arena* absl_nonnull arena() const { return arena_; }
+
  protected:
   std::string DebugString() const override { return value_.DebugString(); }
 
@@ -296,6 +300,41 @@ CustomListValue WrapLegacyParsedJsonList(ParsedJsonListValue value,
                          arena);
 }
 
+ListValue FromLegacyList(
+    const google::api::expr::runtime::CelList* absl_nullable cel_list) {
+  if (cel_list != nullptr) {
+    NativeTypeId native_type_id = NativeTypeId::Of(*cel_list);
+    if (native_type_id ==
+        NativeTypeId::For<LegacyParsedRepeatedFieldListValue>()) {
+      const auto* impl =
+          cel::internal::down_cast<const LegacyParsedRepeatedFieldListValue*>(
+              cel_list);
+      return CustomListValue(impl, impl->arena());
+    }
+    if (native_type_id == NativeTypeId::For<LegacyParsedJsonListValue>()) {
+      const auto* impl =
+          cel::internal::down_cast<const LegacyParsedJsonListValue*>(cel_list);
+      return CustomListValue(impl, impl->arena());
+    }
+    if (native_type_id == NativeTypeId::For<CompatListValue>()) {
+      const auto* impl =
+          cel::internal::down_cast<const CompatListValue*>(cel_list);
+      if (google::protobuf::Arena* arena = impl->GetOwningArena(); arena != nullptr) {
+        return CustomListValue(impl, arena);
+      }
+      return CustomListValue();
+    }
+    if (native_type_id == NativeTypeId::For<MutableCompatListValue>()) {
+      const auto* impl =
+          cel::internal::down_cast<const MutableCompatListValue*>(cel_list);
+      if (google::protobuf::Arena* arena = impl->GetOwningArena(); arena != nullptr) {
+        return CustomListValue(impl, arena);
+      }
+    }
+  }
+  return LegacyListValue(cel_list);
+}
+
 absl::Status LegacyListValue::Equal(
     const Value& other,
     const google::protobuf::DescriptorPool* absl_nonnull descriptor_pool,
diff --git a/common/values/legacy_list_value.h b/common/values/legacy_list_value.h
index 6dd6a568e..55a169653 100644
--- a/common/values/legacy_list_value.h
+++ b/common/values/legacy_list_value.h
@@ -171,6 +171,9 @@ CustomListValue WrapLegacyParsedRepeatedField(
 CustomListValue WrapLegacyParsedJsonList(ParsedJsonListValue value,
                                          google::protobuf::Arena* absl_nonnull arena);
 
+ListValue FromLegacyList(
+    const google::api::expr::runtime::CelList* absl_nullable cel_list);
+
 }  // namespace common_internal
 
 }  // namespace cel
diff --git a/common/values/legacy_map_value.cc b/common/values/legacy_map_value.cc
index 8d9ce2ad3..bd025c51b 100644
--- a/common/values/legacy_map_value.cc
+++ b/common/values/legacy_map_value.cc
@@ -253,11 +253,10 @@ class LegacyParsedMapFieldMapValue final
       const google::api::expr::runtime::CelValue& key) const override {
     CEL_RETURN_IF_ERROR(
         google::api::expr::runtime::CelValue::CheckMapKeyType(key));
-    google::protobuf::Arena scratch_arena;
     Value modern_key;
-    CEL_RETURN_IF_ERROR(ModernValue(&scratch_arena, key, modern_key));
+    CEL_RETURN_IF_ERROR(ModernValue(arena_, key, modern_key));
     return Has(modern_key, google::protobuf::DescriptorPool::generated_pool(),
-               google::protobuf::MessageFactory::generated_factory(), &scratch_arena);
+               google::protobuf::MessageFactory::generated_factory(), arena_);
   }
 
   absl::StatusOr<const google::api::expr::runtime::CelList*> ListKeys()
@@ -281,6 +280,8 @@ class LegacyParsedMapFieldMapValue final
     return legacy_list->cel_list();
   }
 
+  google::protobuf::Arena* absl_nonnull arena() const { return arena_; }
+
  private:
   NativeTypeId GetNativeTypeId() const override {
     return NativeTypeId::For<LegacyParsedMapFieldMapValue>();
@@ -440,11 +441,10 @@ class LegacyParsedJsonMapValue final
       const google::api::expr::runtime::CelValue& key) const override {
     CEL_RETURN_IF_ERROR(
         google::api::expr::runtime::CelValue::CheckMapKeyType(key));
-    google::protobuf::Arena scratch_arena;
     Value modern_key;
-    CEL_RETURN_IF_ERROR(ModernValue(&scratch_arena, key, modern_key));
+    CEL_RETURN_IF_ERROR(ModernValue(arena_, key, modern_key));
     return Has(modern_key, google::protobuf::DescriptorPool::generated_pool(),
-               google::protobuf::MessageFactory::generated_factory(), &scratch_arena);
+               google::protobuf::MessageFactory::generated_factory(), arena_);
   }
 
   absl::StatusOr<const google::api::expr::runtime::CelList*> ListKeys()
@@ -468,6 +468,8 @@ class LegacyParsedJsonMapValue final
     return legacy_list->cel_list();
   }
 
+  google::protobuf::Arena* absl_nonnull arena() const { return arena_; }
+
  private:
   NativeTypeId GetNativeTypeId() const override {
     return NativeTypeId::For<LegacyParsedJsonMapValue>();
@@ -491,6 +493,40 @@ CustomMapValue WrapLegacyParsedJsonMap(ParsedJsonMapValue value,
                         arena);
 }
 
+MapValue FromLegacyMap(
+    const google::api::expr::runtime::CelMap* absl_nullable cel_map) {
+  if (cel_map != nullptr) {
+    NativeTypeId native_type_id = NativeTypeId::Of(*cel_map);
+    if (native_type_id == NativeTypeId::For<LegacyParsedMapFieldMapValue>()) {
+      const auto* impl =
+          cel::internal::down_cast<const LegacyParsedMapFieldMapValue*>(
+              cel_map);
+      return CustomMapValue(impl, impl->arena());
+    }
+    if (native_type_id == NativeTypeId::For<LegacyParsedJsonMapValue>()) {
+      const auto* impl =
+          cel::internal::down_cast<const LegacyParsedJsonMapValue*>(cel_map);
+      return CustomMapValue(impl, impl->arena());
+    }
+    if (native_type_id == NativeTypeId::For<CompatMapValue>()) {
+      const auto* impl =
+          cel::internal::down_cast<const CompatMapValue*>(cel_map);
+      if (google::protobuf::Arena* arena = impl->GetOwningArena(); arena != nullptr) {
+        return CustomMapValue(impl, arena);
+      }
+      return CustomMapValue();
+    }
+    if (native_type_id == NativeTypeId::For<MutableCompatMapValue>()) {
+      const auto* impl =
+          cel::internal::down_cast<const MutableCompatMapValue*>(cel_map);
+      if (google::protobuf::Arena* arena = impl->GetOwningArena(); arena != nullptr) {
+        return CustomMapValue(impl, arena);
+      }
+    }
+  }
+  return LegacyMapValue(cel_map);
+}
+
 absl::Status LegacyMapValue::Equal(
     const Value& other,
     const google::protobuf::DescriptorPool* absl_nonnull descriptor_pool,
diff --git a/common/values/legacy_map_value.h b/common/values/legacy_map_value.h
index 53f39a8de..c170dea80 100644
--- a/common/values/legacy_map_value.h
+++ b/common/values/legacy_map_value.h
@@ -188,6 +188,9 @@ CustomMapValue WrapLegacyParsedMapField(ParsedMapFieldValue value,
 CustomMapValue WrapLegacyParsedJsonMap(ParsedJsonMapValue value,
                                        google::protobuf::Arena* absl_nonnull arena);
 
+MapValue FromLegacyMap(
+    const google::api::expr::runtime::CelMap* absl_nullable cel_map);
+
 }  // namespace common_internal
 
 }  // namespace cel