diff --git a/src/libcore/os.rs b/src/libcore/os.rs
index d068841bc531..2d6c021faa5b 100644
--- a/src/libcore/os.rs
+++ b/src/libcore/os.rs
@@ -96,7 +96,7 @@ mod win32 {
         let mut done = false;
         while !done {
             let buf = vec::to_mut(vec::from_elem(n as uint, 0u16));
-            do vec::as_mut_buf(buf) |b| {
+            do vec::as_mut_buf(buf) |b, _sz| {
                 let k : dword = f(b, tmpbuf_sz as dword);
                 if k == (0 as dword) {
                     done = true;
diff --git a/src/libcore/run.rs b/src/libcore/run.rs
index 9f3da0672536..40b1d1a2d263 100644
--- a/src/libcore/run.rs
+++ b/src/libcore/run.rs
@@ -136,7 +136,7 @@ fn with_envp<T>(env: option<~[(~str,~str)]>,
                 ::unsafe::forget(v);
             }
             blk += ~[0_u8];
-            vec::as_buf(blk, |p| cb(::unsafe::reinterpret_cast(p)))
+            vec::as_buf(blk, |p, _len| cb(::unsafe::reinterpret_cast(p)))
           }
           _ {
             cb(ptr::null())