diff --git a/src/libcore/core.rs b/src/libcore/core.rs
index 8681f7d2a1ca..4b07e2b29b7b 100644
--- a/src/libcore/core.rs
+++ b/src/libcore/core.rs
@@ -11,6 +11,7 @@ import vec_iter::extensions;
 import option::extensions;
 import option_iter::extensions;
 import ptr::extensions;
+import rand::extensions;
 
 export path, option, some, none, unreachable;
 export extensions;
diff --git a/src/libcore/rand.rs b/src/libcore/rand.rs
index a2e985ba0088..30ec17990921 100644
--- a/src/libcore/rand.rs
+++ b/src/libcore/rand.rs
@@ -1,6 +1,6 @@
 #[doc = "Random number generation"];
 
-export rng;
+export rng, extensions;
 
 enum rctx {}
 
@@ -15,55 +15,56 @@ native mod rustrt {
 iface rng {
     #[doc = "Return the next random integer"]
     fn next() -> u32;
-
-    #[doc = "Return the next random float"]
-    fn next_float() -> float;
-
-    #[doc = "Return a random string composed of A-Z, a-z, 0-9."]
-    fn gen_str(len: uint) -> str;
-
-    #[doc = "Return a random byte string."]
-    fn gen_bytes(len: uint) -> [u8];
 }
 
-resource rand_res(c: *rctx) { rustrt::rand_free(c); }
+#[doc = "Extension methods for random number generators"]
+impl extensions for rng {
+
+    #[doc = "Return a random float"]
+    fn gen_float() -> float {
+          let u1 = self.next() as float;
+          let u2 = self.next() as float;
+          let u3 = self.next() as float;
+          let scale = u32::max_value as float;
+          ret ((u1 / scale + u2) / scale + u3) / scale;
+    }
+
+    #[doc = "Return a random string composed of A-Z, a-z, 0-9."]
+    fn gen_str(len: uint) -> str {
+        let charset = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
+                      "abcdefghijklmnopqrstuvwxyz" +
+                      "0123456789";
+        let mut s = "";
+        let mut i = 0u;
+        while (i < len) {
+            let n = self.next() as uint % charset.len();
+            s = s + str::from_char(str::char_at(charset, n));
+            i += 1u;
+        }
+        s
+    }
+
+    #[doc = "Return a random byte string."]
+    fn gen_bytes(len: uint) -> [u8] {
+        let mut v = [];
+        let mut i = 0u;
+        while i < len {
+            let n = self.next() as uint;
+            v += [(n % (u8::max_value as uint)) as u8];
+            i += 1u;
+        }
+        v
+    }
+}
 
 #[doc = "Create a random number generator"]
 fn rng() -> rng {
+    resource rand_res(c: *rctx) { rustrt::rand_free(c); }
+
     impl of rng for @rand_res {
         fn next() -> u32 { ret rustrt::rand_next(**self); }
-        fn next_float() -> float {
-          let u1 = rustrt::rand_next(**self) as float;
-          let u2 = rustrt::rand_next(**self) as float;
-          let u3 = rustrt::rand_next(**self) as float;
-          let scale = u32::max_value as float;
-          ret ((u1 / scale + u2) / scale + u3) / scale;
-        }
-        fn gen_str(len: uint) -> str {
-            let charset = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" +
-                          "abcdefghijklmnopqrstuvwxyz" +
-                          "0123456789";
-            let mut s = "";
-            let mut i = 0u;
-            while (i < len) {
-                let n = rustrt::rand_next(**self) as uint %
-                    str::len(charset);
-                s = s + str::from_char(str::char_at(charset, n));
-                i += 1u;
-            }
-            s
-        }
-        fn gen_bytes(len: uint) -> [u8] {
-            let mut v = [];
-            let mut i = 0u;
-            while i < len {
-                let n = rustrt::rand_next(**self) as uint;
-                v += [(n % (u8::max_value as uint)) as u8];
-                i += 1u;
-            }
-            v
-        }
     }
+
     @rand_res(rustrt::rand_new()) as rng
 }
 
@@ -72,7 +73,7 @@ mod tests {
 
     #[test]
     fn test() {
-        let r1: rand::rng = rand::rng();
+        let r1 = rand::rng();
         log(debug, r1.next());
         log(debug, r1.next());
         {
@@ -95,13 +96,30 @@ mod tests {
     }
 
     #[test]
-    fn genstr() {
-        let r: rand::rng = rand::rng();
+    fn gen_float() {
+        let r = rand::rng();
+        let a = r.gen_float();
+        let b = r.gen_float();
+        log(debug, (a, b));
+    }
+
+    #[test]
+    fn gen_str() {
+        let r = rand::rng();
         log(debug, r.gen_str(10u));
         log(debug, r.gen_str(10u));
         log(debug, r.gen_str(10u));
-        assert(str::len(r.gen_str(10u)) == 10u);
-        assert(str::len(r.gen_str(16u)) == 16u);
+        assert r.gen_str(0u).len() == 0u;
+        assert r.gen_str(10u).len() == 10u;
+        assert r.gen_str(16u).len() == 16u;
+    }
+
+    #[test]
+    fn gen_bytes() {
+        let r = rand::rng();
+        assert r.gen_bytes(0u).len() == 0u;
+        assert r.gen_bytes(10u).len() == 10u;
+        assert r.gen_bytes(16u).len() == 16u;
     }
 }