diff --git a/src/lib/rand.rs b/src/lib/rand.rs
index fee8bbe06bae..b4e5ebc3058f 100644
--- a/src/lib/rand.rs
+++ b/src/lib/rand.rs
@@ -14,6 +14,7 @@ native "rust" mod rustrt {
 type rng =
     obj {
         fn next() -> u32;
+        fn next_float() -> float;
     };
 
 resource rand_res(c: rustrt::rctx) { rustrt::rand_free(c); }
@@ -21,6 +22,13 @@ resource rand_res(c: rustrt::rctx) { rustrt::rand_free(c); }
 fn mk_rng() -> rng {
     obj rt_rng(c: @rand_res) {
         fn next() -> u32 { ret rustrt::rand_next(**c); }
+        fn next_float() -> float {
+          let u1 = rustrt::rand_next(**c) as float;
+          let u2 = rustrt::rand_next(**c) as float;
+          let u3 = rustrt::rand_next(**c) as float;
+          let scale = u32::max_value() as float;
+          ret ((u1 / scale + u2) / scale + u3) / scale;
+        }
     }
     ret rt_rng(@rand_res(rustrt::rand_new()));
 }