diff --git a/source/chapter2/05_Control_Flow.md b/source/chapter2/05_Control_Flow.md
index 8ee3f8de..79e52d6d 100755
--- a/source/chapter2/05_Control_Flow.md
+++ b/source/chapter2/05_Control_Flow.md
@@ -568,7 +568,7 @@ for character in puzzleInput {
     case "a", "e", "i", "o", "u", " ":
         continue
     default:
-        puzzleOutput += character
+        puzzleOutput.append(character)
     }
 }
 println(puzzleOutput)