diff --git a/modules/openapi-generator/src/main/resources/dart2/api.mustache b/modules/openapi-generator/src/main/resources/dart2/api.mustache
index e40ebac3940..c6289c2b766 100644
--- a/modules/openapi-generator/src/main/resources/dart2/api.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/api.mustache
@@ -176,7 +176,7 @@ class {{{classname}}} {
       final responseBody = await _decodeBodyBytes(response);
       return (await apiClient.deserializeAsync(responseBody, '{{{returnType}}}') as List)
         .cast<{{{returnBaseType}}}>()
-        .{{#uniqueItems}}toSet(){{/uniqueItems}}{{^uniqueItems}}toList(){{/uniqueItems}};
+        .{{#uniqueItems}}toSet(){{/uniqueItems}}{{^uniqueItems}}toList(growable: false){{/uniqueItems}};
     {{/isArray}}
     {{^isArray}}
     {{#isMap}}
diff --git a/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache b/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache
index a8dc4df18f7..a8a6273cf28 100644
--- a/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache
+++ b/modules/openapi-generator/src/main/resources/dart2/serialization/native/native_class.mustache
@@ -86,7 +86,7 @@ class {{{classname}}} {
     {{/isDate}}
     {{^isDateTime}}
       {{^isDate}}
-      json[r'{{{baseName}}}'] = this.{{{name}}};
+      json[r'{{{baseName}}}'] = this.{{{name}}}{{#isArray}}{{#uniqueItems}}{{#isNullable}}!{{/isNullable}}.toList(growable: false){{/uniqueItems}}{{/isArray}};
       {{/isDate}}
     {{/isDateTime}}
     {{#isNullable}}
@@ -200,8 +200,8 @@ class {{{classname}}} {
         {{{name}}}: {{{items.datatypeWithEnum}}}.listFromJson(json[r'{{{baseName}}}']){{#uniqueItems}}.toSet(){{/uniqueItems}},
             {{/isEnum}}
             {{^isEnum}}
-        {{{name}}}: json[r'{{{baseName}}}'] is {{#uniqueItems}}Set{{/uniqueItems}}{{^uniqueItems}}List{{/uniqueItems}}
-            ? (json[r'{{{baseName}}}'] as {{#uniqueItems}}Set{{/uniqueItems}}{{^uniqueItems}}List{{/uniqueItems}}).cast<{{{items.datatype}}}>()
+        {{{name}}}: json[r'{{{baseName}}}'] is Iterable
+            ? (json[r'{{{baseName}}}'] as Iterable).cast<{{{items.datatype}}}>().{{#uniqueItems}}toSet(){{/uniqueItems}}{{^uniqueItems}}toList(growable: false){{/uniqueItems}}
             : {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}},
             {{/isEnum}}
           {{/isArray}}
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api/pet_api.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api/pet_api.dart
index d0354de38db..68cb08b13e9 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api/pet_api.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/api/pet_api.dart
@@ -190,7 +190,7 @@ class PetApi {
       final responseBody = await _decodeBodyBytes(response);
       return (await apiClient.deserializeAsync(responseBody, 'List<Pet>') as List)
         .cast<Pet>()
-        .toList();
+        .toList(growable: false);
 
     }
     return null;
@@ -253,7 +253,7 @@ class PetApi {
       final responseBody = await _decodeBodyBytes(response);
       return (await apiClient.deserializeAsync(responseBody, 'List<Pet>') as List)
         .cast<Pet>()
-        .toList();
+        .toList(growable: false);
 
     }
     return null;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart
index 53a2d20dcec..a8e54d9920f 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib/lib/model/pet.dart
@@ -113,8 +113,8 @@ class Pet {
         id: mapValueOfType<int>(json, r'id'),
         category: Category.fromJson(json[r'category']),
         name: mapValueOfType<String>(json, r'name')!,
-        photoUrls: json[r'photoUrls'] is List
-            ? (json[r'photoUrls'] as List).cast<String>()
+        photoUrls: json[r'photoUrls'] is Iterable
+            ? (json[r'photoUrls'] as Iterable).cast<String>().toList(growable: false)
             : const [],
         tags: Tag.listFromJson(json[r'tags']),
         status: PetStatusEnum.fromJson(json[r'status']),
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api/pet_api.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api/pet_api.dart
index 371afa625cf..2f49efb4c3f 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api/pet_api.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/api/pet_api.dart
@@ -182,7 +182,7 @@ class PetApi {
       final responseBody = await _decodeBodyBytes(response);
       return (await apiClient.deserializeAsync(responseBody, 'List<Pet>') as List)
         .cast<Pet>()
-        .toList();
+        .toList(growable: false);
 
     }
     return null;
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_number_only.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_number_only.dart
index 65a8d4b14d1..9275a619a5a 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_number_only.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_of_number_only.dart
@@ -55,8 +55,8 @@ class ArrayOfNumberOnly {
       }());
 
       return ArrayOfNumberOnly(
-        arrayNumber: json[r'ArrayNumber'] is List
-            ? (json[r'ArrayNumber'] as List).cast<num>()
+        arrayNumber: json[r'ArrayNumber'] is Iterable
+            ? (json[r'ArrayNumber'] as Iterable).cast<num>().toList(growable: false)
             : const [],
       );
     }
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_test.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_test.dart
index 1d4114defe6..282d225cfa6 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_test.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/array_test.dart
@@ -67,8 +67,8 @@ class ArrayTest {
       }());
 
       return ArrayTest(
-        arrayOfString: json[r'array_of_string'] is List
-            ? (json[r'array_of_string'] as List).cast<String>()
+        arrayOfString: json[r'array_of_string'] is Iterable
+            ? (json[r'array_of_string'] as Iterable).cast<String>().toList(growable: false)
             : const [],
         arrayArrayOfInteger: json[r'array_array_of_integer'] is List
           ? (json[r'array_array_of_integer'] as List).map((e) =>
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/object_with_deprecated_fields.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/object_with_deprecated_fields.dart
index 2e2e2b7c687..91932b3bc41 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/object_with_deprecated_fields.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/object_with_deprecated_fields.dart
@@ -108,8 +108,8 @@ class ObjectWithDeprecatedFields {
             ? null
             : num.parse(json[r'id'].toString()),
         deprecatedRef: DeprecatedObject.fromJson(json[r'deprecatedRef']),
-        bars: json[r'bars'] is List
-            ? (json[r'bars'] as List).cast<String>()
+        bars: json[r'bars'] is Iterable
+            ? (json[r'bars'] as Iterable).cast<String>().toList(growable: false)
             : const [],
       );
     }
diff --git a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/pet.dart b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/pet.dart
index 669bf85edd5..9e0c77e120b 100644
--- a/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/pet.dart
+++ b/samples/openapi3/client/petstore/dart2/petstore_client_lib_fake/lib/model/pet.dart
@@ -81,7 +81,7 @@ class Pet {
       json[r'category'] = null;
     }
       json[r'name'] = this.name;
-      json[r'photoUrls'] = this.photoUrls;
+      json[r'photoUrls'] = this.photoUrls.toList(growable: false);
       json[r'tags'] = this.tags;
     if (this.status != null) {
       json[r'status'] = this.status;
@@ -113,8 +113,8 @@ class Pet {
         id: mapValueOfType<int>(json, r'id'),
         category: Category.fromJson(json[r'category']),
         name: mapValueOfType<String>(json, r'name')!,
-        photoUrls: json[r'photoUrls'] is Set
-            ? (json[r'photoUrls'] as Set).cast<String>()
+        photoUrls: json[r'photoUrls'] is Iterable
+            ? (json[r'photoUrls'] as Iterable).cast<String>().toSet()
             : const {},
         tags: Tag.listFromJson(json[r'tags']),
         status: PetStatusEnum.fromJson(json[r'status']),