diff --git a/TECHDEBT.md b/TECHDEBT.md
index c4d43ae..edf371b 100644
--- a/TECHDEBT.md
+++ b/TECHDEBT.md
@@ -6,6 +6,14 @@
   - [ ] data class
   - [ ] message chain
 
+# Mikado
+- [ ] Change var to val (immutable)
+  - [ ] Rover.turnLeft use copy() on state
+  - [ ] Rover.turnRight use copy() on state
+  - [ ] Rover.move use copy() on state
+  - [ ] Rover.constructor use copy() on state
+    - [ ] Change RoverState to Data Class
+
 # RPP
 - [ ] Refine Abstractions
   - [ ] long parameter list
diff --git a/src/main/kotlin/org/example/RoverState.kt b/src/main/kotlin/org/example/RoverState.kt
index 2dc282c..f0af6ed 100644
--- a/src/main/kotlin/org/example/RoverState.kt
+++ b/src/main/kotlin/org/example/RoverState.kt
@@ -1,7 +1,7 @@
 package org.example
 
-class RoverState {
-    var positionX: Int = 0
-    var positionY: Int = 0
-    var heading: Heading = Heading.NORTH
-}
+data class RoverState(
+    var positionX: Int = 0,
+    var positionY: Int = 0,
+    var heading: Heading = Heading.NORTH,
+)