diff --git a/codegen/end_to_end_test_tristate/build.yaml b/codegen/end_to_end_test_tristate/build.yaml
index 34f5af92..06b2243a 100644
--- a/codegen/end_to_end_test_tristate/build.yaml
+++ b/codegen/end_to_end_test_tristate/build.yaml
@@ -12,16 +12,21 @@ targets:
         options:
           schema: end_to_end_test_tristate|lib/graphql/schema.graphql
           custom_serializers:
-            - import: 'package:end_to_end_test_tristate/date_serializer.dart'
+            - import: "package:end_to_end_test_tristate/date_serializer.dart"
               name: DateSerializer
-            - import: 'package:end_to_end_test_tristate/custom_field_serializer.dart'
+            - import: "package:end_to_end_test_tristate/custom_field_serializer.dart"
               name: CustomFieldSerializer
+            - import: "package:end_to_end_test_tristate/custom_date_serializer.dart"
+              name: CustomDateSerializer
           type_overrides:
-            Date:
+            DateTime:
               name: DateTime
             CustomField:
               name: CustomField
-              import: 'package:end_to_end_test_tristate/custom_field.dart'
+              import: "package:end_to_end_test_tristate/custom_field.dart"
+            Date:
+              name: CustomDate
+              import: "package:end_to_end_test_tristate/custom_date.dart"
       gql_build|schema_builder:
         enabled: true
         options:
@@ -29,11 +34,14 @@ targets:
           enum_fallbacks:
             LengthUnit: METER
           type_overrides:
-            Date:
+            DateTime:
               name: DateTime
             CustomField:
               name: CustomField
-              import: 'package:end_to_end_test_tristate/custom_field.dart'
+              import: "package:end_to_end_test_tristate/custom_field.dart"
+            Date:
+              name: CustomDate
+              import: "package:end_to_end_test_tristate/custom_date.dart"
       gql_build|data_builder:
         enabled: true
         options:
@@ -42,11 +50,14 @@ targets:
             when: true
             maybeWhen: true
           type_overrides:
-            Date:
+            DateTime:
               name: DateTime
             CustomField:
               name: CustomField
-              import: 'package:end_to_end_test_tristate/custom_field.dart'
+              import: "package:end_to_end_test_tristate/custom_field.dart"
+            Date:
+              name: CustomDate
+              import: "package:end_to_end_test_tristate/custom_date.dart"
       gql_build|var_builder:
         enabled: true
         options:
@@ -54,8 +65,11 @@ targets:
           tristate_optionals: true
           vars_create_factories: true
           type_overrides:
-            Date:
+            DateTime:
               name: DateTime
             CustomField:
               name: CustomField
-              import: 'package:end_to_end_test_tristate/custom_field.dart'
+              import: "package:end_to_end_test_tristate/custom_field.dart"
+            Date:
+              name: CustomDate
+              import: "package:end_to_end_test_tristate/custom_date.dart"
diff --git a/codegen/end_to_end_test_tristate/lib/custom_date.dart b/codegen/end_to_end_test_tristate/lib/custom_date.dart
new file mode 100644
index 00000000..52f308d5
--- /dev/null
+++ b/codegen/end_to_end_test_tristate/lib/custom_date.dart
@@ -0,0 +1,19 @@
+class CustomDate extends DateTime {
+  CustomDate(
+    super.year,
+    super.month,
+    super.day,
+  );
+
+  static CustomDate parse(String formattedString) {
+    final DateTime dateTime = DateTime.parse(formattedString);
+    return CustomDate(dateTime.year, dateTime.month, dateTime.day);
+  }
+
+  @override
+  CustomDate toLocal() {
+    final DateTime localDateTime = super.toLocal();
+    return CustomDate(
+        localDateTime.year, localDateTime.month, localDateTime.day);
+  }
+}
diff --git a/codegen/end_to_end_test_tristate/lib/custom_date_serializer.dart b/codegen/end_to_end_test_tristate/lib/custom_date_serializer.dart
new file mode 100644
index 00000000..51f1349e
--- /dev/null
+++ b/codegen/end_to_end_test_tristate/lib/custom_date_serializer.dart
@@ -0,0 +1,30 @@
+import 'package:built_value/serializer.dart';
+import 'package:end_to_end_test_tristate/custom_date.dart';
+
+class CustomDateSerializer implements PrimitiveSerializer<CustomDate> {
+  @override
+  CustomDate deserialize(
+    Serializers serializers,
+    Object serialized, {
+    FullType specifiedType = FullType.unspecified,
+  }) {
+    assert(serialized is String,
+        "CustomDateSerializer expected 'String' but got ${serialized.runtimeType}");
+    return CustomDate.parse(serialized as String).toLocal();
+  }
+
+  @override
+  String serialize(
+    Serializers serializers,
+    CustomDate date, {
+    FullType specifiedType = FullType.unspecified,
+  }) {
+    return date.toUtc().toIso8601String().split('T').first;
+  }
+
+  @override
+  Iterable<Type> get types => [CustomDate];
+
+  @override
+  String get wireName => 'Date';
+}
diff --git a/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.ast.gql.dart b/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.ast.gql.dart
index 3b75b47a..57843f51 100644
--- a/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.ast.gql.dart
+++ b/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.ast.gql.dart
@@ -247,7 +247,7 @@ const Mutation = _i1.ObjectTypeDefinitionNode(
           name: _i1.NameNode(value: 'createdAt'),
           directives: [],
           type: _i1.NamedTypeNode(
-            name: _i1.NameNode(value: 'Date'),
+            name: _i1.NameNode(value: 'DateTime'),
             isNonNull: false,
           ),
           defaultValue: null,
@@ -790,7 +790,7 @@ const Review = _i1.ObjectTypeDefinitionNode(
       directives: [],
       args: [],
       type: _i1.NamedTypeNode(
-        name: _i1.NameNode(value: 'Date'),
+        name: _i1.NameNode(value: 'DateTime'),
         isNonNull: false,
       ),
     ),
@@ -800,7 +800,7 @@ const Review = _i1.ObjectTypeDefinitionNode(
       args: [],
       type: _i1.ListTypeNode(
         type: _i1.NamedTypeNode(
-          name: _i1.NameNode(value: 'Date'),
+          name: _i1.NameNode(value: 'DateTime'),
           isNonNull: true,
         ),
         isNonNull: true,
@@ -856,13 +856,22 @@ const ReviewInput = _i1.InputObjectTypeDefinitionNode(
       directives: [],
       type: _i1.ListTypeNode(
         type: _i1.NamedTypeNode(
-          name: _i1.NameNode(value: 'Date'),
+          name: _i1.NameNode(value: 'DateTime'),
           isNonNull: false,
         ),
         isNonNull: false,
       ),
       defaultValue: null,
     ),
+    _i1.InputValueDefinitionNode(
+      name: _i1.NameNode(value: 'createdDay'),
+      directives: [],
+      type: _i1.NamedTypeNode(
+        name: _i1.NameNode(value: 'Date'),
+        isNonNull: true,
+      ),
+      defaultValue: null,
+    ),
   ],
 );
 const CustomFieldInput = _i1.InputObjectTypeDefinitionNode(
@@ -1133,6 +1142,10 @@ const SearchResult = _i1.UnionTypeDefinitionNode(
     ),
   ],
 );
+const DateTime = _i1.ScalarTypeDefinitionNode(
+  name: _i1.NameNode(value: 'DateTime'),
+  directives: [],
+);
 const Date = _i1.ScalarTypeDefinitionNode(
   name: _i1.NameNode(value: 'Date'),
   directives: [],
@@ -1174,6 +1187,7 @@ const document = _i1.DocumentNode(definitions: [
   PostLikesInput,
   PostFavoritesInput,
   SearchResult,
+  DateTime,
   Date,
   ISODate,
   CustomField,
diff --git a/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.schema.gql.dart b/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.schema.gql.dart
index a4d268dc..2065dcd6 100644
--- a/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.schema.gql.dart
+++ b/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.schema.gql.dart
@@ -5,11 +5,12 @@
 import 'package:built_collection/built_collection.dart';
 import 'package:built_value/built_value.dart';
 import 'package:built_value/serializer.dart';
-import 'package:end_to_end_test_tristate/custom_field.dart' as _i2;
+import 'package:end_to_end_test_tristate/custom_date.dart' as _i2;
+import 'package:end_to_end_test_tristate/custom_field.dart' as _i3;
 import 'package:end_to_end_test_tristate/graphql/__generated__/serializers.gql.dart'
-    as _i3;
-import 'package:gql_code_builder/src/serializers/default_scalar_serializer.dart'
     as _i4;
+import 'package:gql_code_builder/src/serializers/default_scalar_serializer.dart'
+    as _i5;
 import 'package:gql_tristate_value/gql_tristate_value.dart' as _i1;
 
 part 'schema.schema.gql.g.dart';
@@ -64,13 +65,14 @@ abstract class GReviewInput
   _i1.Value<String> get commentary;
   _i1.Value<GColorInput> get favorite_color;
   _i1.Value<BuiltList<DateTime?>> get seenOn;
-  Map<String, dynamic> toJson() => (_i3.serializers.serializeWith(
+  _i2.CustomDate get createdDay;
+  Map<String, dynamic> toJson() => (_i4.serializers.serializeWith(
         GReviewInput.serializer,
         this,
       ) as Map<String, dynamic>);
 
   static GReviewInput? fromJson(Map<String, dynamic> json) =>
-      _i3.serializers.deserializeWith(
+      _i4.serializers.deserializeWith(
         GReviewInput.serializer,
         json,
       );
@@ -111,6 +113,9 @@ final class GReviewInputSerializer extends StructuredSerializer<GReviewInput> {
       result.add(serializers.serialize(_$value,
           specifiedType: const FullType(BuiltList, [FullType(DateTime)])));
     }
+    result.add('createdDay');
+    result.add(serializers.serialize(object.createdDay,
+        specifiedType: const FullType(_i2.CustomDate)));
     return result;
   }
 
@@ -148,6 +153,11 @@ final class GReviewInputSerializer extends StructuredSerializer<GReviewInput> {
               as BuiltList<DateTime>;
           builder.seenOn = _i1.PresentValue(_$fieldValue);
           break;
+        case 'createdDay':
+          var _$fieldValue = serializers.deserialize(value,
+              specifiedType: const FullType(_i2.CustomDate)) as _i2.CustomDate;
+          builder.createdDay = _$fieldValue;
+          break;
       }
     }
     return builder.build();
@@ -166,14 +176,14 @@ abstract class GCustomFieldInput
       b..customField = const _i1.AbsentValue();
 
   String get id;
-  _i1.Value<_i2.CustomField> get customField;
-  Map<String, dynamic> toJson() => (_i3.serializers.serializeWith(
+  _i1.Value<_i3.CustomField> get customField;
+  Map<String, dynamic> toJson() => (_i4.serializers.serializeWith(
         GCustomFieldInput.serializer,
         this,
       ) as Map<String, dynamic>);
 
   static GCustomFieldInput? fromJson(Map<String, dynamic> json) =>
-      _i3.serializers.deserializeWith(
+      _i4.serializers.deserializeWith(
         GCustomFieldInput.serializer,
         json,
       );
@@ -202,7 +212,7 @@ final class GCustomFieldInputSerializer
     if (_$customFieldvalue case _i1.PresentValue(value: final _$value)) {
       result.add('customField');
       result.add(serializers.serialize(_$value,
-          specifiedType: const FullType(_i2.CustomField)));
+          specifiedType: const FullType(_i3.CustomField)));
     }
     return result;
   }
@@ -226,8 +236,8 @@ final class GCustomFieldInputSerializer
           break;
         case 'customField':
           var _$fieldValue = serializers.deserialize(value,
-                  specifiedType: const FullType(_i2.CustomField))
-              as _i2.CustomField;
+                  specifiedType: const FullType(_i3.CustomField))
+              as _i3.CustomField;
           builder.customField = _i1.PresentValue(_$fieldValue);
           break;
       }
@@ -245,13 +255,13 @@ abstract class GColorInput implements Built<GColorInput, GColorInputBuilder> {
   int get red;
   int get green;
   int get blue;
-  Map<String, dynamic> toJson() => (_i3.serializers.serializeWith(
+  Map<String, dynamic> toJson() => (_i4.serializers.serializeWith(
         GColorInput.serializer,
         this,
       ) as Map<String, dynamic>);
 
   static GColorInput? fromJson(Map<String, dynamic> json) =>
-      _i3.serializers.deserializeWith(
+      _i4.serializers.deserializeWith(
         GColorInput.serializer,
         json,
       );
@@ -324,13 +334,13 @@ abstract class GPostLikesInput
       _$GPostLikesInput;
 
   String get id;
-  Map<String, dynamic> toJson() => (_i3.serializers.serializeWith(
+  Map<String, dynamic> toJson() => (_i4.serializers.serializeWith(
         GPostLikesInput.serializer,
         this,
       ) as Map<String, dynamic>);
 
   static GPostLikesInput? fromJson(Map<String, dynamic> json) =>
-      _i3.serializers.deserializeWith(
+      _i4.serializers.deserializeWith(
         GPostLikesInput.serializer,
         json,
       );
@@ -390,13 +400,13 @@ abstract class GPostFavoritesInput
       _$GPostFavoritesInput;
 
   String get id;
-  Map<String, dynamic> toJson() => (_i3.serializers.serializeWith(
+  Map<String, dynamic> toJson() => (_i4.serializers.serializeWith(
         GPostFavoritesInput.serializer,
         this,
       ) as Map<String, dynamic>);
 
   static GPostFavoritesInput? fromJson(Map<String, dynamic> json) =>
-      _i3.serializers.deserializeWith(
+      _i4.serializers.deserializeWith(
         GPostFavoritesInput.serializer,
         json,
       );
@@ -459,7 +469,7 @@ abstract class GISODate implements Built<GISODate, GISODateBuilder> {
   String get value;
   @BuiltValueSerializer(custom: true)
   static Serializer<GISODate> get serializer =>
-      _i4.DefaultScalarSerializer<GISODate>(
+      _i5.DefaultScalarSerializer<GISODate>(
           (Object serialized) => GISODate((serialized as String?)));
 }
 
@@ -471,7 +481,7 @@ abstract class GJson implements Built<GJson, GJsonBuilder> {
 
   String get value;
   @BuiltValueSerializer(custom: true)
-  static Serializer<GJson> get serializer => _i4.DefaultScalarSerializer<GJson>(
+  static Serializer<GJson> get serializer => _i5.DefaultScalarSerializer<GJson>(
       (Object serialized) => GJson((serialized as String?)));
 }
 
diff --git a/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.schema.gql.g.dart b/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.schema.gql.g.dart
index 8368dc16..b7979beb 100644
--- a/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.schema.gql.g.dart
+++ b/codegen/end_to_end_test_tristate/lib/graphql/__generated__/schema.schema.gql.g.dart
@@ -104,6 +104,8 @@ class _$GReviewInput extends GReviewInput {
   final _i1.Value<GColorInput> favorite_color;
   @override
   final _i1.Value<BuiltList<DateTime?>> seenOn;
+  @override
+  final _i2.CustomDate createdDay;
 
   factory _$GReviewInput([void Function(GReviewInputBuilder)? updates]) =>
       (new GReviewInputBuilder()..update(updates))._build();
@@ -112,7 +114,8 @@ class _$GReviewInput extends GReviewInput {
       {required this.stars,
       required this.commentary,
       required this.favorite_color,
-      required this.seenOn})
+      required this.seenOn,
+      required this.createdDay})
       : super._() {
     BuiltValueNullFieldError.checkNotNull(stars, r'GReviewInput', 'stars');
     BuiltValueNullFieldError.checkNotNull(
@@ -120,6 +123,8 @@ class _$GReviewInput extends GReviewInput {
     BuiltValueNullFieldError.checkNotNull(
         favorite_color, r'GReviewInput', 'favorite_color');
     BuiltValueNullFieldError.checkNotNull(seenOn, r'GReviewInput', 'seenOn');
+    BuiltValueNullFieldError.checkNotNull(
+        createdDay, r'GReviewInput', 'createdDay');
   }
 
   @override
@@ -136,7 +141,8 @@ class _$GReviewInput extends GReviewInput {
         stars == other.stars &&
         commentary == other.commentary &&
         favorite_color == other.favorite_color &&
-        seenOn == other.seenOn;
+        seenOn == other.seenOn &&
+        createdDay == other.createdDay;
   }
 
   @override
@@ -146,6 +152,7 @@ class _$GReviewInput extends GReviewInput {
     _$hash = $jc(_$hash, commentary.hashCode);
     _$hash = $jc(_$hash, favorite_color.hashCode);
     _$hash = $jc(_$hash, seenOn.hashCode);
+    _$hash = $jc(_$hash, createdDay.hashCode);
     _$hash = $jf(_$hash);
     return _$hash;
   }
@@ -156,7 +163,8 @@ class _$GReviewInput extends GReviewInput {
           ..add('stars', stars)
           ..add('commentary', commentary)
           ..add('favorite_color', favorite_color)
-          ..add('seenOn', seenOn))
+          ..add('seenOn', seenOn)
+          ..add('createdDay', createdDay))
         .toString();
   }
 }
@@ -184,6 +192,10 @@ class GReviewInputBuilder
   set seenOn(_i1.Value<BuiltList<DateTime?>>? seenOn) =>
       _$this._seenOn = seenOn;
 
+  _i2.CustomDate? _createdDay;
+  _i2.CustomDate? get createdDay => _$this._createdDay;
+  set createdDay(_i2.CustomDate? createdDay) => _$this._createdDay = createdDay;
+
   GReviewInputBuilder() {
     GReviewInput._initializeBuilder(this);
   }
@@ -195,6 +207,7 @@ class GReviewInputBuilder
       _commentary = $v.commentary;
       _favorite_color = $v.favorite_color;
       _seenOn = $v.seenOn;
+      _createdDay = $v.createdDay;
       _$v = null;
     }
     return this;
@@ -224,7 +237,9 @@ class GReviewInputBuilder
             favorite_color: BuiltValueNullFieldError.checkNotNull(
                 favorite_color, r'GReviewInput', 'favorite_color'),
             seenOn: BuiltValueNullFieldError.checkNotNull(
-                seenOn, r'GReviewInput', 'seenOn'));
+                seenOn, r'GReviewInput', 'seenOn'),
+            createdDay: BuiltValueNullFieldError.checkNotNull(
+                createdDay, r'GReviewInput', 'createdDay'));
     replace(_$result);
     return _$result;
   }
@@ -234,7 +249,7 @@ class _$GCustomFieldInput extends GCustomFieldInput {
   @override
   final String id;
   @override
-  final _i1.Value<_i2.CustomField> customField;
+  final _i1.Value<_i3.CustomField> customField;
 
   factory _$GCustomFieldInput(
           [void Function(GCustomFieldInputBuilder)? updates]) =>
@@ -289,9 +304,9 @@ class GCustomFieldInputBuilder
   String? get id => _$this._id;
   set id(String? id) => _$this._id = id;
 
-  _i1.Value<_i2.CustomField>? _customField;
-  _i1.Value<_i2.CustomField>? get customField => _$this._customField;
-  set customField(_i1.Value<_i2.CustomField>? customField) =>
+  _i1.Value<_i3.CustomField>? _customField;
+  _i1.Value<_i3.CustomField>? get customField => _$this._customField;
+  set customField(_i1.Value<_i3.CustomField>? customField) =>
       _$this._customField = customField;
 
   GCustomFieldInputBuilder() {
diff --git a/codegen/end_to_end_test_tristate/lib/graphql/__generated__/serializers.gql.dart b/codegen/end_to_end_test_tristate/lib/graphql/__generated__/serializers.gql.dart
index 15090df8..227f8ae5 100644
--- a/codegen/end_to_end_test_tristate/lib/graphql/__generated__/serializers.gql.dart
+++ b/codegen/end_to_end_test_tristate/lib/graphql/__generated__/serializers.gql.dart
@@ -23,6 +23,9 @@ import 'package:end_to_end_test_tristate/aliases/__generated__/aliased_hero.req.
     show GAliasedHero;
 import 'package:end_to_end_test_tristate/aliases/__generated__/aliased_hero.var.gql.dart'
     show GAliasedHeroVars;
+import 'package:end_to_end_test_tristate/custom_date.dart';
+import 'package:end_to_end_test_tristate/custom_date_serializer.dart'
+    show CustomDateSerializer;
 import 'package:end_to_end_test_tristate/custom_field.dart';
 import 'package:end_to_end_test_tristate/custom_field_serializer.dart'
     show CustomFieldSerializer;
@@ -154,6 +157,7 @@ final SerializersBuilder _serializersBuilder = _$serializers.toBuilder()
   ..add(OperationSerializer())
   ..add(DateSerializer())
   ..add(CustomFieldSerializer())
+  ..add(CustomDateSerializer())
   ..add(GHeroForEpisodeData_hero.serializer)
   ..add(GheroFieldsFragmentData.serializer)
   ..add(GheroFieldsFragmentData__asHuman_friends.serializer)
diff --git a/codegen/end_to_end_test_tristate/lib/graphql/schema.graphql b/codegen/end_to_end_test_tristate/lib/graphql/schema.graphql
index 671605a7..67cc84f5 100644
--- a/codegen/end_to_end_test_tristate/lib/graphql/schema.graphql
+++ b/codegen/end_to_end_test_tristate/lib/graphql/schema.graphql
@@ -8,7 +8,6 @@ schema {
 
 directive @extends on OBJECT | INTERFACE
 
-
 # The query type, represents all of the entry points into our object graph
 type Query {
   hero(episode: Episode): Character
@@ -23,7 +22,11 @@ type Query {
 
 # The mutation type, represents all updates we can make to our data
 type Mutation {
-  createReview(episode: Episode, review: ReviewInput!, createdAt: Date): Review
+  createReview(
+    episode: Episode
+    review: ReviewInput!
+    createdAt: DateTime
+  ): Review
   createCustomField(input: CustomFieldInput!): CustomField
 }
 
@@ -140,9 +143,9 @@ type Review {
   # Comment about the movie
   commentary: String
   # Date review created
-  createdAt: Date
+  createdAt: DateTime
   # Date episode seen
-  seenOn: [Date!]!
+  seenOn: [DateTime!]!
   # A custom field
   custom: [CustomField!]!
 }
@@ -156,7 +159,9 @@ input ReviewInput {
   # Favorite color, optional
   favorite_color: ColorInput
   # Date viewed
-  seenOn: [Date]
+  seenOn: [DateTime]
+  # Use of a custom scalar.
+  createdDay: Date!
 }
 
 input CustomFieldInput {
@@ -206,7 +211,9 @@ input PostFavoritesInput {
 
 union SearchResult = Human | Droid | Starship
 
+scalar DateTime
 scalar Date
+
 scalar ISODate
 scalar CustomField
 
diff --git a/codegen/end_to_end_test_tristate/lib/scalars/__generated__/review_with_date.ast.gql.dart b/codegen/end_to_end_test_tristate/lib/scalars/__generated__/review_with_date.ast.gql.dart
index d3b70e19..f19bfdf2 100644
--- a/codegen/end_to_end_test_tristate/lib/scalars/__generated__/review_with_date.ast.gql.dart
+++ b/codegen/end_to_end_test_tristate/lib/scalars/__generated__/review_with_date.ast.gql.dart
@@ -29,7 +29,7 @@ const ReviewWithDate = _i1.OperationDefinitionNode(
     _i1.VariableDefinitionNode(
       variable: _i1.VariableNode(name: _i1.NameNode(value: 'createdAt')),
       type: _i1.NamedTypeNode(
-        name: _i1.NameNode(value: 'Date'),
+        name: _i1.NameNode(value: 'DateTime'),
         isNonNull: false,
       ),
       defaultValue: _i1.DefaultValueNode(value: null),
diff --git a/codegen/end_to_end_test_tristate/lib/scalars/review_with_date.graphql b/codegen/end_to_end_test_tristate/lib/scalars/review_with_date.graphql
index 5cad0ddd..2fd250e1 100644
--- a/codegen/end_to_end_test_tristate/lib/scalars/review_with_date.graphql
+++ b/codegen/end_to_end_test_tristate/lib/scalars/review_with_date.graphql
@@ -1,7 +1,7 @@
 mutation ReviewWithDate(
   $episode: Episode
   $review: ReviewInput!
-  $createdAt: Date
+  $createdAt: DateTime
 ) {
   createReview(episode: $episode, review: $review, createdAt: $createdAt) {
     episode
diff --git a/codegen/gql_code_builder/lib/src/tristate_optionals.dart b/codegen/gql_code_builder/lib/src/tristate_optionals.dart
index c4d01d99..9abdb3f3 100644
--- a/codegen/gql_code_builder/lib/src/tristate_optionals.dart
+++ b/codegen/gql_code_builder/lib/src/tristate_optionals.dart
@@ -181,13 +181,10 @@ String _generateFieldDeserializers(
         type = (type as TypeReference).types.first;
       }
       final fullType = _generateFullType(type as TypeReference, allocator);
-
-      /// remove the leading `G` from the type name
-      /// TODO refactor this
-      final originalSymbolName = type.symbol.substring(1);
-
-      final typeDefNode =
-          getTypeDefinitionNode(schemaSource.document, originalSymbolName);
+      final typeDefNode = getTypeDefinitionNode(
+        schemaSource.document,
+        _originalSymbolName(typeOverrides, type),
+      );
 
       //TODO this feels flaky, find a better way
       final isBuilder = type.url != null &&
@@ -198,7 +195,6 @@ String _generateFieldDeserializers(
       const fieldNameVariableName = "_\$fieldValue";
 
       final fieldNameExpr = CodeExpression(Code(fieldNameVariableName));
-
       var base = """
 case '${_getWireName(field)}':
   var ${fieldNameVariableName} = serializers.deserialize(
@@ -220,6 +216,26 @@ break;
 """;
     }).join();
 
+String _originalSymbolName(
+    Map<String, Reference> typeOverrides, TypeReference type) {
+  String? originalSymbolName;
+
+  /// If symbol exists in [typeOverrides] then the original symbol from Schema file is the key of [typeOverrides].
+  /// And [type.symbol] is the type of the Dart class that handles Schema's scalar.
+  for (final entry in typeOverrides.entries) {
+    if (entry.value.symbol == type.symbol) {
+      originalSymbolName = entry.key;
+      break;
+    }
+  }
+
+  /// Removes the leading `G` from the type name.
+  /// It still can not work if you original type's symbol starts with the 'G' letter.
+  originalSymbolName ??=
+      type.symbol[0] == "G" ? type.symbol.substring(1) : type.symbol;
+  return originalSymbolName;
+}
+
 String _getWireName(Method m) {
   final wireNameExpr = m.annotations
       .map((annotation) {