diff --git a/src/libstd/os.rs b/src/libstd/os.rs
index 78cae2964570c..69d51025234c8 100644
--- a/src/libstd/os.rs
+++ b/src/libstd/os.rs
@@ -53,6 +53,8 @@ use ptr::RawPtr;
 
 #[cfg(unix)]
 use c_str::ToCStr;
+#[cfg(windows)]
+use str::OwnedStr;
 
 /// Delegates to the libc close() function, returning the same return value.
 pub fn close(fd: int) -> int {
@@ -722,10 +724,12 @@ pub fn get_exit_status() -> int {
 }
 
 #[cfg(target_os = "macos")]
-unsafe fn load_argc_and_argv(argc: int, argv: **c_char) -> ~[~str] {
+unsafe fn load_argc_and_argv(argc: int, argv: **c_char) -> ~[~[u8]] {
+    use c_str::CString;
+
     let mut args = ~[];
     for i in range(0u, argc as uint) {
-        args.push(str::raw::from_c_str(*argv.offset(i as int)));
+        args.push(CString::new(*argv.offset(i as int), false).as_bytes_no_nul().to_owned())
     }
     args
 }
@@ -736,7 +740,7 @@ unsafe fn load_argc_and_argv(argc: int, argv: **c_char) -> ~[~str] {
  * Returns a list of the command line arguments.
  */
 #[cfg(target_os = "macos")]
-fn real_args() -> ~[~str] {
+fn real_args_as_bytes() -> ~[~[u8]] {
     unsafe {
         let (argc, argv) = (*_NSGetArgc() as int,
                             *_NSGetArgv() as **c_char);
@@ -747,7 +751,7 @@ fn real_args() -> ~[~str] {
 #[cfg(target_os = "linux")]
 #[cfg(target_os = "android")]
 #[cfg(target_os = "freebsd")]
-fn real_args() -> ~[~str] {
+fn real_args_as_bytes() -> ~[~[u8]] {
     use rt;
 
     match rt::args::clone() {
@@ -756,6 +760,11 @@ fn real_args() -> ~[~str] {
     }
 }
 
+#[cfg(not(windows))]
+fn real_args() -> ~[~str] {
+    real_args_as_bytes().move_iter().map(|v| str::from_utf8_lossy(v).into_owned()).collect()
+}
+
 #[cfg(windows)]
 fn real_args() -> ~[~str] {
     use vec;
@@ -786,6 +795,11 @@ fn real_args() -> ~[~str] {
     return args;
 }
 
+#[cfg(windows)]
+fn real_args_as_bytes() -> ~[~[u8]] {
+    real_args().move_iter().map(|s| s.into_bytes()).collect()
+}
+
 type LPCWSTR = *u16;
 
 #[cfg(windows)]
@@ -803,10 +817,19 @@ extern "system" {
 
 /// Returns the arguments which this program was started with (normally passed
 /// via the command line).
+///
+/// The arguments are interpreted as utf-8, with invalid bytes replaced with \uFFFD.
+/// See `str::from_utf8_lossy` for details.
 pub fn args() -> ~[~str] {
     real_args()
 }
 
+/// Returns the arguments which this program was started with (normally passed
+/// via the command line) as byte vectors.
+pub fn args_as_bytes() -> ~[~[u8]] {
+    real_args_as_bytes()
+}
+
 #[cfg(target_os = "macos")]
 extern {
     // These functions are in crt_externs.h.
diff --git a/src/libstd/rt/args.rs b/src/libstd/rt/args.rs
index cef03d66923af..c417ea375fd38 100644
--- a/src/libstd/rt/args.rs
+++ b/src/libstd/rt/args.rs
@@ -36,8 +36,8 @@ pub unsafe fn init(argc: int, argv: **u8) { realargs::init(argc, argv) }
 #[cfg(test)]      pub unsafe fn cleanup() { realargs::cleanup() }
 
 /// Take the global arguments from global storage.
-#[cfg(not(test))] pub fn take() -> Option<~[~str]> { imp::take() }
-#[cfg(test)]      pub fn take() -> Option<~[~str]> {
+#[cfg(not(test))] pub fn take() -> Option<~[~[u8]]> { imp::take() }
+#[cfg(test)]      pub fn take() -> Option<~[~[u8]]> {
     match realargs::take() {
         realstd::option::Some(a) => Some(a),
         realstd::option::None => None,
@@ -47,12 +47,12 @@ pub unsafe fn init(argc: int, argv: **u8) { realargs::init(argc, argv) }
 /// Give the global arguments to global storage.
 ///
 /// It is an error if the arguments already exist.
-#[cfg(not(test))] pub fn put(args: ~[~str]) { imp::put(args) }
-#[cfg(test)]      pub fn put(args: ~[~str]) { realargs::put(args) }
+#[cfg(not(test))] pub fn put(args: ~[~[u8]]) { imp::put(args) }
+#[cfg(test)]      pub fn put(args: ~[~[u8]]) { realargs::put(args) }
 
 /// Make a clone of the global arguments.
-#[cfg(not(test))] pub fn clone() -> Option<~[~str]> { imp::clone() }
-#[cfg(test)]      pub fn clone() -> Option<~[~str]> {
+#[cfg(not(test))] pub fn clone() -> Option<~[~[u8]]> { imp::clone() }
+#[cfg(test)]      pub fn clone() -> Option<~[~[u8]]> {
     match realargs::clone() {
         realstd::option::Some(a) => Some(a),
         realstd::option::None => None,
@@ -65,15 +65,12 @@ pub unsafe fn init(argc: int, argv: **u8) { realargs::init(argc, argv) }
 mod imp {
     use cast;
     use clone::Clone;
-    #[cfg(not(test))] use libc;
     use option::{Option, Some, None};
     use ptr::RawPtr;
     use iter::Iterator;
-    #[cfg(not(test))] use str;
     use unstable::finally::Finally;
     use unstable::mutex::{Mutex, MUTEX_INIT};
     use mem;
-    #[cfg(not(test))] use vec;
 
     static mut global_args_ptr: uint = 0;
     static mut lock: Mutex = MUTEX_INIT;
@@ -90,15 +87,15 @@ mod imp {
         lock.destroy();
     }
 
-    pub fn take() -> Option<~[~str]> {
+    pub fn take() -> Option<~[~[u8]]> {
         with_lock(|| unsafe {
             let ptr = get_global_ptr();
             let val = mem::replace(&mut *ptr, None);
-            val.as_ref().map(|s: &~~[~str]| (**s).clone())
+            val.as_ref().map(|s: &~~[~[u8]]| (**s).clone())
         })
     }
 
-    pub fn put(args: ~[~str]) {
+    pub fn put(args: ~[~[u8]]) {
         with_lock(|| unsafe {
             let ptr = get_global_ptr();
             rtassert!((*ptr).is_none());
@@ -106,10 +103,10 @@ mod imp {
         })
     }
 
-    pub fn clone() -> Option<~[~str]> {
+    pub fn clone() -> Option<~[~[u8]]> {
         with_lock(|| unsafe {
             let ptr = get_global_ptr();
-            (*ptr).as_ref().map(|s: &~~[~str]| (**s).clone())
+            (*ptr).as_ref().map(|s: &~~[~[u8]]| (**s).clone())
         })
     }
 
@@ -126,15 +123,20 @@ mod imp {
         })
     }
 
-    fn get_global_ptr() -> *mut Option<~~[~str]> {
+    fn get_global_ptr() -> *mut Option<~~[~[u8]]> {
         unsafe { cast::transmute(&global_args_ptr) }
     }
 
     // Copied from `os`.
     #[cfg(not(test))]
-    unsafe fn load_argc_and_argv(argc: int, argv: **u8) -> ~[~str] {
+    unsafe fn load_argc_and_argv(argc: int, argv: **u8) -> ~[~[u8]] {
+        use c_str::CString;
+        use {vec, libc};
+        use vec::CloneableVector;
+
         vec::from_fn(argc as uint, |i| {
-            str::raw::from_c_str(*(argv as **libc::c_char).offset(i as int))
+            let cs = CString::new(*(argv as **libc::c_char).offset(i as int), false);
+            cs.as_bytes_no_nul().to_owned()
         })
     }
 
@@ -149,7 +151,7 @@ mod imp {
             // Preserve the actual global state.
             let saved_value = take();
 
-            let expected = ~[~"happy", ~"today?"];
+            let expected = ~[bytes!("happy").to_owned(), bytes!("today?").to_owned()];
 
             put(expected.clone());
             assert!(clone() == Some(expected.clone()));
@@ -179,15 +181,15 @@ mod imp {
     pub fn cleanup() {
     }
 
-    pub fn take() -> Option<~[~str]> {
+    pub fn take() -> Option<~[~[u8]]> {
         fail!()
     }
 
-    pub fn put(_args: ~[~str]) {
+    pub fn put(_args: ~[~[u8]]) {
         fail!()
     }
 
-    pub fn clone() -> Option<~[~str]> {
+    pub fn clone() -> Option<~[~[u8]]> {
         fail!()
     }
 }