diff --git a/libs/robot.lua b/libs/robot.lua
index 0fc7ee8..70afb15 100644
--- a/libs/robot.lua
+++ b/libs/robot.lua
@@ -20,7 +20,7 @@ api.create = function(state, defaultStateFile)
 
   local mutateRobotPosition = function(isBackward)
     local incValue = 1
-    if isBackward then invValue = -1 end
+    if isBackward then incValue = -1 end
 
     if state.dir == 'FORWARD' then
       state.z = state.z + incValue