diff --git a/src/libstd/rand.rs b/src/libstd/rand.rs
index a6c1dca4342f..b763c1c2d761 100644
--- a/src/libstd/rand.rs
+++ b/src/libstd/rand.rs
@@ -25,7 +25,7 @@ distributions like normal and exponential.
 use core::rand::RngUtil;
 
 fn main() {
-    let rng = rand::rng();
+    let mut rng = rand::rng();
     if rng.gen() { // bool
         println(fmt!("int: %d, uint: %u", rng.gen(), rng.gen()))
     }