diff --git a/lib/generators/json_serializable_generator.dart b/lib/generators/json_serializable_generator.dart
index 36f7a18c..16c7f205 100644
--- a/lib/generators/json_serializable_generator.dart
+++ b/lib/generators/json_serializable_generator.dart
@@ -204,7 +204,7 @@ class JsonSerializableGenerator
       }
     }
 
-    if (_implementsDartList(fieldType)) {
+    if (_coreListChecker.isAssignableFromType(fieldType)) {
       var indexVal = "i${depth}";
 
       var substitute = '${expression}[$indexVal]';
@@ -247,7 +247,7 @@ class JsonSerializableGenerator
       }
     }
 
-    if (_isDartIterable(searchType) || _isDartList(searchType)) {
+    if (_coreIterableChecker.isAssignableFromType(searchType)) {
       var iterableGenericType =
           _getIterableGenericType(searchType as InterfaceType);
 
@@ -257,7 +257,7 @@ class JsonSerializableGenerator
           "${_writeAccessToVar(itemVal, iterableGenericType, depth: depth+1)}"
           ")";
 
-      if (_isDartList(searchType)) {
+      if (_coreListChecker.isAssignableFromType(searchType)) {
         output += "?.toList()";
       }
 
@@ -287,24 +287,24 @@ String _fieldToJsonMapKey(String fieldName, FieldElement field) {
 }
 
 DartType _getIterableGenericType(InterfaceType type) {
-  var iterableThing = _typeTest(type, _isDartIterable) as InterfaceType;
+  var iterableImplementation =
+      _getImplementationType(type, _coreIterableChecker) as InterfaceType;
 
-  return iterableThing.typeArguments.single;
+  return iterableImplementation.typeArguments.single;
 }
 
-bool _implementsDartList(DartType type) => _typeTest(type, _isDartList) != null;
-
-DartType _typeTest(DartType type, bool tester(DartType type)) {
-  if (tester(type)) return type;
+DartType _getImplementationType(DartType type, TypeChecker checker) {
+  if (checker.isExactlyType(type)) return type;
 
   if (type is InterfaceType) {
-    var tests = type.interfaces.map((type) => _typeTest(type, tester));
+    var tests =
+        type.interfaces.map((type) => _getImplementationType(type, checker));
     var match = _firstNotNull(tests);
 
     if (match != null) return match;
 
     if (type.superclass != null) {
-      return _typeTest(type.superclass, tester);
+      return _getImplementationType(type.superclass, checker);
     }
   }
   return null;
@@ -313,8 +313,6 @@ DartType _typeTest(DartType type, bool tester(DartType type)) {
 T _firstNotNull<T>(Iterable<T> values) =>
     values.firstWhere((value) => value != null, orElse: () => null);
 
-bool _isDartIterable(DartType type) =>
-    const TypeChecker.fromUrl('dart:core#Iterable').isExactlyType(type);
+final _coreIterableChecker = const TypeChecker.fromUrl('dart:core#Iterable');
 
-bool _isDartList(DartType type) =>
-    const TypeChecker.fromUrl('dart:core#List').isExactlyType(type);
+final _coreListChecker = const TypeChecker.fromUrl('dart:core#List');
diff --git a/lib/src/json_serializable/type_helper.dart b/lib/src/json_serializable/type_helper.dart
index fdcd8c22..23d7154f 100644
--- a/lib/src/json_serializable/type_helper.dart
+++ b/lib/src/json_serializable/type_helper.dart
@@ -4,6 +4,7 @@
 
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
+import 'package:source_gen/src/type_checker.dart';
 
 abstract class TypeHelper {
   const TypeHelper();
@@ -104,7 +105,7 @@ class DateTimeHelper extends TypeHelper {
   bool canDeserialize(DartType type) => _matchesType(type);
 
   bool _matchesType(DartType type) =>
-      type.element.library?.isDartCore == true && type.name == 'DateTime';
+      const TypeChecker.fromUrl('dart:core#DateTime').isExactlyType(type);
 
   @override
   String serialize(DartType targetType, String name) =>
diff --git a/lib/src/type_checker.dart b/lib/src/type_checker.dart
index 794ddbde..3af42b16 100644
--- a/lib/src/type_checker.dart
+++ b/lib/src/type_checker.dart
@@ -46,6 +46,16 @@ abstract class TypeChecker {
       .map((a) => a.computeConstantValue())
       .where((a) => isExactlyType(a.type));
 
+  /// Returns `true` if representing the exact same class an or a superclass of
+  /// [element]
+  bool isAssignableFrom(Element element) =>
+      isExactly(element) || isSuperOf(element);
+
+  /// Returns `true` if representing the exact same type as or a supertype of
+  /// [staticType].
+  bool isAssignableFromType(DartType staticType) =>
+      isAssignableFrom(staticType.element);
+
   /// Returns `true` if representing the exact same class as [element].
   bool isExactly(Element element);
 
diff --git a/test/type_checker_test.dart b/test/type_checker_test.dart
index e5c95364..5988ec4d 100644
--- a/test/type_checker_test.dart
+++ b/test/type_checker_test.dart
@@ -52,6 +52,10 @@ void main() {
       test('should be a super type of dart:collection#HashMap', () {
         expect(checkMap().isSuperTypeOf(staticHashMap), isTrue);
       });
+
+      test('should be assignable from dart:collection#HashMap', () {
+        expect(checkMap().isAssignableFromType(staticHashMap), isTrue);
+      });
     });
 
     group('(HashMap)', () {
@@ -63,6 +67,10 @@ void main() {
       test('should not be a super type of dart:core#Map', () {
         expect(checkHashMap().isSuperTypeOf(staticMap), isFalse);
       });
+
+      test('should not assignable from type dart:core#Map', () {
+        expect(checkHashMap().isAssignableFromType(staticMap), isFalse);
+      });
     });
   }