diff --git a/src/libcore/io.rs b/src/libcore/io.rs
index 5d42012dcce..01edaeabe05 100644
--- a/src/libcore/io.rs
+++ b/src/libcore/io.rs
@@ -317,7 +317,7 @@ impl of writer for *libc::FILE {
             let nout = libc::fwrite(vbuf as *c_void, len, 1u, self);
             if nout < 1 as size_t {
                 #error("error writing buffer");
-                log(error, sys::last_os_error());
+                log(error, os::last_os_error());
                 fail;
             }
         }
@@ -348,7 +348,7 @@ impl of writer for fd_t {
                 let nout = libc::write(self, vb, len);
                 if nout < 0 as ssize_t {
                     #error("error writing buffer");
-                    log(error, sys::last_os_error());
+                    log(error, os::last_os_error());
                     fail;
                 }
                 count += nout as uint;
@@ -402,7 +402,7 @@ fn mk_file_writer(path: str, flags: [fileflag])
                    (S_IRUSR | S_IWUSR) as c_int)
     };
     if fd < (0 as c_int) {
-        result::err(#fmt("error opening %s: %s", path, sys::last_os_error()))
+        result::err(#fmt("error opening %s: %s", path, os::last_os_error()))
     } else {
         result::ok(fd_writer(fd, true))
     }
diff --git a/src/libcore/os.rs b/src/libcore/os.rs
index 1df34e5f393..6c5e4181ab5 100644
--- a/src/libcore/os.rs
+++ b/src/libcore/os.rs
@@ -32,6 +32,7 @@ export exe_suffix, dll_suffix, sysname;
 export homedir, list_dir, list_dir_path, path_is_dir, path_exists,
        make_absolute, make_dir, remove_dir, change_dir, remove_file,
        copy_file;
+export last_os_error;
 
 // FIXME: move these to str perhaps?
 export as_c_charp, fill_charp_buf;
@@ -43,6 +44,7 @@ native mod rustrt {
     fn rust_path_exists(path: *libc::c_char) -> c_int;
     fn rust_list_files(path: str) -> [str];
     fn rust_process_wait(handle: c_int) -> c_int;
+    fn last_os_error() -> str;
 }
 
 
@@ -623,6 +625,10 @@ fn remove_file(p: path) -> bool {
     }
 }
 
+#[doc = "Get a string representing the platform-dependent last error"]
+fn last_os_error() -> str {
+    rustrt::last_os_error()
+}
 
 
 #[cfg(target_os = "macos")]
@@ -659,6 +665,10 @@ mod consts {
 #[cfg(test)]
 mod tests {
 
+    #[test]
+    fn last_os_error() {
+        log(debug, last_os_error());
+    }
 
     fn make_rand_name() -> str {
         import rand;
diff --git a/src/libcore/sys.rs b/src/libcore/sys.rs
index 77634ab77ca..ce83ab596e2 100644
--- a/src/libcore/sys.rs
+++ b/src/libcore/sys.rs
@@ -2,7 +2,6 @@
 
 export type_desc;
 export get_type_desc;
-export last_os_error;
 export size_of;
 export align_of;
 export refcount;
@@ -18,10 +17,6 @@ enum type_desc = {
 
 #[abi = "cdecl"]
 native mod rustrt {
-    // Explicitly re-export native stuff we want to be made
-    // available outside this crate. Otherwise it's
-    // visible-in-crate, but not re-exported.
-    fn last_os_error() -> str;
     fn refcount<T>(t: @T) -> libc::intptr_t;
     fn unsupervise();
     fn shape_log_str<T>(t: *sys::type_desc, data: T) -> str;
@@ -45,11 +40,6 @@ fn get_type_desc<T>() -> *type_desc {
     rusti::get_tydesc::<T>() as *type_desc
 }
 
-#[doc = "Get a string representing the platform-dependent last error"]
-fn last_os_error() -> str {
-    rustrt::last_os_error()
-}
-
 #[doc = "Returns the size of a type"]
 fn size_of<T>() -> uint unsafe {
     rusti::size_of::<T>()
@@ -84,11 +74,6 @@ fn set_exit_status(code: int) {
 #[cfg(test)]
 mod tests {
 
-    #[test]
-    fn last_os_error() {
-        log(debug, last_os_error());
-    }
-
     #[test]
     fn size_of_basic() {
         assert size_of::<u8>() == 1u;