diff --git a/lib/ckb/serializers/output_serializer.rb b/lib/ckb/serializers/output_serializer.rb
index f04c2526..636b83b3 100644
--- a/lib/ckb/serializers/output_serializer.rb
+++ b/lib/ckb/serializers/output_serializer.rb
@@ -23,7 +23,7 @@ def layout
 
       def body
         result = capacity_layout + lock_script_layout
-        result + type_script_layout if type_script_serializer
+        result += type_script_layout if type_script_serializer
 
         result
       end