diff --git a/src/robot.rs b/src/robot.rs
index da57e61..59fa0bd 100644
--- a/src/robot.rs
+++ b/src/robot.rs
@@ -1,7 +1,7 @@
 /// A Robot *aka droid* is represented here.
 /// Each robot must have a unique id.
 pub struct Robot {
-    id: i32,
+    id: u32,
     o: Orientation,
     p: Position,
     i: Vec<char>,