diff --git a/src/libcore/comm.rs b/src/libcore/comm.rs
index 072562233de..5b2bb3a132f 100644
--- a/src/libcore/comm.rs
+++ b/src/libcore/comm.rs
@@ -234,8 +234,9 @@ impl<T: Owned> Selectable for Port<T> {
 }
 
 /// Treat many ports as one.
+#[unsafe_mut_field(ports)]
 pub struct PortSet<T> {
-    mut ports: ~[Port<T>],
+    ports: ~[Port<T>],
 }
 
 pub impl<T: Owned> PortSet<T> {
@@ -246,7 +247,10 @@ pub impl<T: Owned> PortSet<T> {
     }
 
     fn add(&self, port: Port<T>) {
-        self.ports.push(port)
+        unsafe {
+            let self_ports = transmute_mut(&self.ports);
+            self_ports.push(port)
+        }
     }
 
     fn chan(&self) -> Chan<T> {
@@ -258,25 +262,28 @@ pub impl<T: Owned> PortSet<T> {
 
 impl<T:Owned> GenericPort<T> for PortSet<T> {
     fn try_recv(&self) -> Option<T> {
-        let mut result = None;
-        // we have to swap the ports array so we aren't borrowing
-        // aliasable mutable memory.
-        let mut ports = ~[];
-        ports <-> self.ports;
-        while result.is_none() && ports.len() > 0 {
-            let i = wait_many(ports);
-            match ports[i].try_recv() {
-                Some(m) => {
-                    result = Some(m);
-                }
-                None => {
-                    // Remove this port.
-                    let _ = ports.swap_remove(i);
+        unsafe {
+            let mut self_ports = transmute_mut(&self.ports);
+            let mut result = None;
+            // we have to swap the ports array so we aren't borrowing
+            // aliasable mutable memory.
+            let mut ports = ~[];
+            ports <-> *self_ports;
+            while result.is_none() && ports.len() > 0 {
+                let i = wait_many(ports);
+                match ports[i].try_recv() {
+                    Some(m) => {
+                        result = Some(m);
+                    }
+                    None => {
+                        // Remove this port.
+                        let _ = ports.swap_remove(i);
+                    }
                 }
             }
+            ports <-> *self_ports;
+            result
         }
-        ports <-> self.ports;
-        result
     }
     fn recv(&self) -> T {
         self.try_recv().expect("port_set: endpoints closed")
@@ -288,10 +295,9 @@ impl<T: Owned> Peekable<T> for PortSet<T> {
         // It'd be nice to use self.port.each, but that version isn't
         // pure.
         for uint::range(0, vec::uniq_len(&const self.ports)) |i| {
-            // XXX: Botch pending demuting.
-            unsafe {
-                let port: &Port<T> = cast::transmute(&mut self.ports[i]);
-                if port.peek() { return true }
+            let port: &Port<T> = &self.ports[i];
+            if port.peek() {
+                return true;
             }
         }
         false
diff --git a/src/libcore/io.rs b/src/libcore/io.rs
index 64b69a7928b..63335f7e952 100644
--- a/src/libcore/io.rs
+++ b/src/libcore/io.rs
@@ -983,36 +983,50 @@ pub fn file_reader(path: &Path) -> Result<@Reader, ~str> {
 // Byte readers
 pub struct BytesReader<'self> {
     bytes: &'self [u8],
-    mut pos: uint
+    pos: @mut uint
 }
 
 impl<'self> Reader for BytesReader<'self> {
     fn read(&self, bytes: &mut [u8], len: uint) -> uint {
-        let count = uint::min(len, self.bytes.len() - self.pos);
+        let count = uint::min(len, self.bytes.len() - *self.pos);
 
-        let view = vec::slice(self.bytes, self.pos, self.bytes.len());
+        let view = vec::slice(self.bytes, *self.pos, self.bytes.len());
         vec::bytes::copy_memory(bytes, view, count);
 
-        self.pos += count;
+        *self.pos += count;
 
         count
     }
+
     fn read_byte(&self) -> int {
-        if self.pos == self.bytes.len() { return -1; }
-        let b = self.bytes[self.pos];
-        self.pos += 1u;
-        return b as int;
+        if *self.pos == self.bytes.len() {
+            return -1;
+        }
+
+        let b = self.bytes[*self.pos];
+        *self.pos += 1u;
+        b as int
     }
-    fn eof(&self) -> bool { self.pos == self.bytes.len() }
+
+    fn eof(&self) -> bool {
+        *self.pos == self.bytes.len()
+    }
+
     fn seek(&self, offset: int, whence: SeekStyle) {
-        let pos = self.pos;
-        self.pos = seek_in_buf(offset, pos, self.bytes.len(), whence);
+        let pos = *self.pos;
+        *self.pos = seek_in_buf(offset, pos, self.bytes.len(), whence);
+    }
+
+    fn tell(&self) -> uint {
+        *self.pos
     }
-    fn tell(&self) -> uint { self.pos }
 }
 
-pub fn with_bytes_reader<t>(bytes: &[u8], f: &fn(@Reader) -> t) -> t {
-    f(@BytesReader { bytes: bytes, pos: 0u } as @Reader)
+pub fn with_bytes_reader<T>(bytes: &[u8], f: &fn(@Reader) -> T) -> T {
+    f(@BytesReader {
+        bytes: bytes,
+        pos: @mut 0
+    } as @Reader)
 }
 
 pub fn with_str_reader<T>(s: &str, f: &fn(@Reader) -> T) -> T {
@@ -1498,49 +1512,67 @@ pub fn buffered_file_writer(path: &Path) -> Result<@Writer, ~str> {
 pub fn stdout() -> @Writer { fd_writer(libc::STDOUT_FILENO as c_int, false) }
 pub fn stderr() -> @Writer { fd_writer(libc::STDERR_FILENO as c_int, false) }
 
-pub fn print(s: &str) { stdout().write_str(s); }
-pub fn println(s: &str) { stdout().write_line(s); }
+pub fn print(s: &str) {
+    stdout().write_str(s);
+}
+
+pub fn println(s: &str) {
+    stdout().write_line(s);
+}
 
 pub struct BytesWriter {
-    mut bytes: ~[u8],
-    mut pos: uint,
+    bytes: @mut ~[u8],
+    pos: @mut uint,
 }
 
 impl Writer for BytesWriter {
     fn write(&self, v: &[u8]) {
         let v_len = v.len();
-        let bytes_len = vec::uniq_len(&const self.bytes);
+        let bytes_len = vec::uniq_len(&const *self.bytes);
 
-        let count = uint::max(bytes_len, self.pos + v_len);
-        vec::reserve(&mut self.bytes, count);
+        let count = uint::max(bytes_len, *self.pos + v_len);
+        vec::reserve(&mut *self.bytes, count);
 
         unsafe {
-            vec::raw::set_len(&mut self.bytes, count);
-            let view = vec::mut_slice(self.bytes, self.pos, count);
+            vec::raw::set_len(&mut *self.bytes, count);
+            let view = vec::mut_slice(*self.bytes, *self.pos, count);
             vec::bytes::copy_memory(view, v, v_len);
         }
 
-        self.pos += v_len;
+        *self.pos += v_len;
     }
+
     fn seek(&self, offset: int, whence: SeekStyle) {
-        let pos = self.pos;
-        let len = vec::uniq_len(&const self.bytes);
-        self.pos = seek_in_buf(offset, pos, len, whence);
+        let pos = *self.pos;
+        let len = vec::uniq_len(&const *self.bytes);
+        *self.pos = seek_in_buf(offset, pos, len, whence);
+    }
+
+    fn tell(&self) -> uint {
+        *self.pos
+    }
+
+    fn flush(&self) -> int {
+        0
+    }
+
+    fn get_type(&self) -> WriterType {
+        File
     }
-    fn tell(&self) -> uint { self.pos }
-    fn flush(&self) -> int { 0 }
-    fn get_type(&self) -> WriterType { File }
 }
 
 pub fn BytesWriter() -> BytesWriter {
-    BytesWriter { bytes: ~[], mut pos: 0u }
+    BytesWriter {
+        bytes: @mut ~[],
+        pos: @mut 0
+    }
 }
 
 pub fn with_bytes_writer(f: &fn(@Writer)) -> ~[u8] {
     let wr = @BytesWriter();
     f(wr as @Writer);
-    let @BytesWriter{bytes, _} = wr;
-    return bytes;
+    let @BytesWriter { bytes, _ } = wr;
+    copy *bytes
 }
 
 pub fn with_str_writer(f: &fn(@Writer)) -> ~str {
@@ -1550,7 +1582,9 @@ pub fn with_str_writer(f: &fn(@Writer)) -> ~str {
     v.push(0);
     assert!(str::is_utf8(v));
 
-    unsafe { ::cast::transmute(v) }
+    unsafe {
+        ::cast::transmute(v)
+    }
 }
 
 // Utility functions
diff --git a/src/librustc/metadata/encoder.rs b/src/librustc/metadata/encoder.rs
index ccf3ffcdfff..c84bebdfd39 100644
--- a/src/librustc/metadata/encoder.rs
+++ b/src/librustc/metadata/encoder.rs
@@ -1372,41 +1372,40 @@ pub fn encode_metadata(parms: EncodeParams, crate: &crate) -> ~[u8] {
 
     encode_hash(&mut ebml_w, ecx.link_meta.extras_hash);
 
-    let mut i = wr.pos;
+    let mut i = *wr.pos;
     let crate_attrs = synthesize_crate_attrs(ecx, crate);
     encode_attributes(&mut ebml_w, crate_attrs);
-    ecx.stats.attr_bytes = wr.pos - i;
+    ecx.stats.attr_bytes = *wr.pos - i;
 
-    i = wr.pos;
+    i = *wr.pos;
     encode_crate_deps(ecx, &mut ebml_w, ecx.cstore);
-    ecx.stats.dep_bytes = wr.pos - i;
+    ecx.stats.dep_bytes = *wr.pos - i;
 
     // Encode the language items.
-    i = wr.pos;
+    i = *wr.pos;
     encode_lang_items(ecx, &mut ebml_w);
-    ecx.stats.lang_item_bytes = wr.pos - i;
+    ecx.stats.lang_item_bytes = *wr.pos - i;
 
     // Encode the link args.
-    i = wr.pos;
+    i = *wr.pos;
     encode_link_args(ecx, &mut ebml_w);
-    ecx.stats.link_args_bytes = wr.pos - i;
+    ecx.stats.link_args_bytes = *wr.pos - i;
 
     // Encode and index the items.
     ebml_w.start_tag(tag_items);
-    i = wr.pos;
+    i = *wr.pos;
     let items_index = encode_info_for_items(ecx, &mut ebml_w, crate);
-    ecx.stats.item_bytes = wr.pos - i;
+    ecx.stats.item_bytes = *wr.pos - i;
 
-    i = wr.pos;
+    i = *wr.pos;
     let items_buckets = create_index(items_index);
     encode_index(&mut ebml_w, items_buckets, write_int);
-    ecx.stats.index_bytes = wr.pos - i;
+    ecx.stats.index_bytes = *wr.pos - i;
     ebml_w.end_tag();
 
-    ecx.stats.total_bytes = wr.pos;
+    ecx.stats.total_bytes = *wr.pos;
 
     if (tcx.sess.meta_stats()) {
-
         do wr.bytes.each |e| {
             if *e == 0 {
                 ecx.stats.zero_bytes += 1;
@@ -1438,9 +1437,11 @@ pub fn encode_metadata(parms: EncodeParams, crate: &crate) -> ~[u8] {
     //
     //   vec::from_slice(metadata_encoding_version) +
 
+    let writer_bytes: &mut ~[u8] = wr.bytes;
+
     (do str::as_bytes(&~"rust\x00\x00\x00\x01") |bytes| {
         vec::slice(*bytes, 0, 8).to_vec()
-    }) + flate::deflate_bytes(wr.bytes)
+    }) + flate::deflate_bytes(*writer_bytes)
 }
 
 // Get the encoded string for a type
diff --git a/src/libstd/io_util.rs b/src/libstd/io_util.rs
index 6ed626202b7..7d43663cc80 100644
--- a/src/libstd/io_util.rs
+++ b/src/libstd/io_util.rs
@@ -29,13 +29,13 @@ pub impl BufReader {
         // I can't get the borrowing to work correctly
         let bytes_reader = BytesReader {
             bytes: ::core::util::id::<&[u8]>(self.buf),
-            pos: *self.pos
+            pos: @mut *self.pos
         };
 
         let res = f(&bytes_reader);
 
         // FIXME #4429: This isn't correct if f fails
-        *self.pos = bytes_reader.pos;
+        *self.pos = *bytes_reader.pos;
 
         return res;
     }