diff --git a/json_serializable/lib/src/type_helpers/enum_helper.dart b/json_serializable/lib/src/type_helpers/enum_helper.dart
index bf1128fcd..a1713fac4 100644
--- a/json_serializable/lib/src/type_helpers/enum_helper.dart
+++ b/json_serializable/lib/src/type_helpers/enum_helper.dart
@@ -43,10 +43,10 @@ class EnumHelper extends TypeHelper<TypeHelperContextWithConfig> {
       return null;
     }
 
-    context.addMember(_enumDecodeHelper);
-
     if (context.nullable) {
       context.addMember(_enumDecodeHelperNullable);
+    } else {
+      context.addMember(_enumDecodeHelper);
     }
 
     context.addMember(memberContent);
@@ -96,14 +96,15 @@ T _$enumDecode<T>(
   }
 
   final value = enumValues.entries
-      .singleWhere((e) => e.value == source, orElse: () => null)
-      ?.key;
+          .singleWhere((e) => e.value == source, orElse: () => null)
+          ?.key ??
+      unknownValue;
 
-  if (value == null && unknownValue == null) {
+  if (value == null) {
     throw ArgumentError('`$source` is not one of the supported values: '
         '${enumValues.values.join(', ')}');
   }
-  return value ?? unknownValue;
+  return value;
 }
 ''';
 
@@ -116,5 +117,7 @@ T _$enumDecodeNullable<T>(
   if (source == null) {
     return null;
   }
-  return _$enumDecode<T>(enumValues, source, unknownValue: unknownValue);
+  return enumValues.entries
+      .singleWhere((e) => e.value == source, orElse: () => null)
+      ?.key ?? unknownValue;
 }''';
diff --git a/json_serializable/test/integration/integration_test.dart b/json_serializable/test/integration/integration_test.dart
index fa51cfbe2..5dbff741b 100644
--- a/json_serializable/test/integration/integration_test.dart
+++ b/json_serializable/test/integration/integration_test.dart
@@ -280,4 +280,18 @@ void main() {
     expect(instance.enumList, [Category.notDiscoveredYet]);
     expect(instance.enumSet, [Category.notDiscoveredYet]);
   });
+
+  test('NullableUnknownEnumValue', () {
+    final instance = NullableUnknownEnumValue.fromJson({
+      'enumValue': 'nope',
+      'enumIterable': ['nope'],
+      'enumList': ['nope'],
+      'enumSet': ['nope'],
+    });
+
+    expect(instance.enumValue, null);
+    expect(instance.enumIterable, [null]);
+    expect(instance.enumList, [null]);
+    expect(instance.enumSet, [null]);
+  });
 }
diff --git a/json_serializable/test/integration/json_test_example.dart b/json_serializable/test/integration/json_test_example.dart
index f23831961..40b867c62 100644
--- a/json_serializable/test/integration/json_test_example.dart
+++ b/json_serializable/test/integration/json_test_example.dart
@@ -194,3 +194,23 @@ class UnknownEnumValue {
   factory UnknownEnumValue.fromJson(Map<String, dynamic> json) =>
       _$UnknownEnumValueFromJson(json);
 }
+
+@JsonSerializable(createToJson: false)
+class NullableUnknownEnumValue {
+  @JsonKey()
+  Category enumValue;
+
+  @JsonKey()
+  Iterable<Category> enumIterable;
+
+  @JsonKey()
+  List<Category> enumList;
+
+  @JsonKey()
+  Set<Category> enumSet;
+
+  NullableUnknownEnumValue();
+
+  factory NullableUnknownEnumValue.fromJson(Map<String, dynamic> json) =>
+      _$NullableUnknownEnumValueFromJson(json);
+}
diff --git a/json_serializable/test/integration/json_test_example.g.dart b/json_serializable/test/integration/json_test_example.g.dart
index 4ec605cc3..6846f70b3 100644
--- a/json_serializable/test/integration/json_test_example.g.dart
+++ b/json_serializable/test/integration/json_test_example.g.dart
@@ -76,7 +76,11 @@ T _$enumDecodeNullable<T>(
   if (source == null) {
     return null;
   }
-  return _$enumDecode<T>(enumValues, source, unknownValue: unknownValue);
+
+  return enumValues.entries
+          .singleWhere((e) => e.value == source, orElse: () => null)
+          ?.key ??
+      unknownValue;
 }
 
 const _$CategoryEnumMap = {
@@ -234,3 +238,17 @@ UnknownEnumValue _$UnknownEnumValueFromJson(Map<String, dynamic> json) {
             unknownValue: Category.notDiscoveredYet))
         ?.toSet();
 }
+
+NullableUnknownEnumValue _$NullableUnknownEnumValueFromJson(
+    Map<String, dynamic> json) {
+  return NullableUnknownEnumValue()
+    ..enumValue = _$enumDecodeNullable(_$CategoryEnumMap, json['enumValue'])
+    ..enumIterable = (json['enumIterable'] as List)
+        .map((e) => _$enumDecodeNullable(_$CategoryEnumMap, e))
+    ..enumList = (json['enumList'] as List)
+        .map((e) => _$enumDecodeNullable(_$CategoryEnumMap, e))
+        .toList()
+    ..enumSet = (json['enumSet'] as List)
+        .map((e) => _$enumDecodeNullable(_$CategoryEnumMap, e))
+        .toSet();
+}