diff --git a/lib/src/class_builder.dart b/lib/src/class_builder.dart
index f8d44d3..f229534 100644
--- a/lib/src/class_builder.dart
+++ b/lib/src/class_builder.dart
@@ -19,8 +19,8 @@ class ClassBuilder extends Builder {
   String buildRead() {
     var code = StringBuffer();
     code.writeln('''
-    var numOfFields = reader.readByte();
-    var fields = <int, dynamic>{
+    final numOfFields = reader.readByte();
+    final fields = <int, dynamic>{
       for (var i = 0; i < numOfFields; i++) reader.readByte(): reader.read(),
     };
     return ${cls.name}(