diff --git a/src/libnative/io/addrinfo.rs b/src/libnative/io/addrinfo.rs
index d40438e4272a3..306c6f5ae14a9 100644
--- a/src/libnative/io/addrinfo.rs
+++ b/src/libnative/io/addrinfo.rs
@@ -106,7 +106,7 @@ fn get_error(s: c_int) -> IoError {
     use std::c_str::CString;
 
     let err_str = unsafe {
-        CString::new(gai_strerror(s), false).as_str().unwrap().to_string()
+        CString::new(gai_strerror(s)).as_str().unwrap().to_string()
     };
     IoError {
         code: s as uint,
diff --git a/src/libnative/io/file_unix.rs b/src/libnative/io/file_unix.rs
index f616295c73d1b..d3995e7893fa3 100644
--- a/src/libnative/io/file_unix.rs
+++ b/src/libnative/io/file_unix.rs
@@ -351,7 +351,7 @@ pub fn readdir(p: &CString) -> IoResult<Vec<CString>> {
     use libc::{opendir, readdir_r, closedir};
 
     fn prune(root: &CString, dirs: Vec<Path>) -> Vec<CString> {
-        let root = unsafe { CString::new(root.as_ptr(), false) };
+        let root = unsafe { CString::new(root.as_ptr()) };
         let root = Path::new(root);
 
         dirs.into_iter().filter(|path| {
@@ -376,7 +376,7 @@ pub fn readdir(p: &CString) -> IoResult<Vec<CString>> {
         while unsafe { readdir_r(dir_ptr, ptr, &mut entry_ptr) == 0 } {
             if entry_ptr.is_null() { break }
             let cstr = unsafe {
-                CString::new(rust_list_dir_val(entry_ptr), false)
+                CString::new(rust_list_dir_val(entry_ptr))
             };
             paths.push(Path::new(cstr));
         }
diff --git a/src/libnative/io/file_windows.rs b/src/libnative/io/file_windows.rs
index eb4d4f22132d0..031fce25f8f16 100644
--- a/src/libnative/io/file_windows.rs
+++ b/src/libnative/io/file_windows.rs
@@ -347,7 +347,7 @@ pub fn mkdir(p: &CString, _mode: uint) -> IoResult<()> {
 
 pub fn readdir(p: &CString) -> IoResult<Vec<CString>> {
     fn prune(root: &CString, dirs: Vec<Path>) -> Vec<CString> {
-        let root = unsafe { CString::new(root.as_ptr(), false) };
+        let root = unsafe { CString::new(root.as_ptr()) };
         let root = Path::new(root);
 
         dirs.into_iter().filter(|path| {
@@ -356,7 +356,7 @@ pub fn readdir(p: &CString) -> IoResult<Vec<CString>> {
     }
 
     let star = Path::new(unsafe {
-        CString::new(p.as_ptr(), false)
+        CString::new(p.as_ptr())
     }).join("*");
     let path = try!(to_utf16(&star.to_c_str()));
 
diff --git a/src/librustc/back/write.rs b/src/librustc/back/write.rs
index 031fc731f41c1..3f7636d0e6475 100644
--- a/src/librustc/back/write.rs
+++ b/src/librustc/back/write.rs
@@ -46,10 +46,10 @@ pub enum OutputType {
 pub fn llvm_err(handler: &diagnostic::Handler, msg: String) -> ! {
     unsafe {
         let cstr = llvm::LLVMRustGetLastError();
-        if cstr == ptr::null() {
+        if cstr as *const i8 == ptr::null() {
             handler.fatal(msg.as_slice());
         } else {
-            let err = CString::new(cstr, true);
+            let err = CString::new_owned(cstr);
             let err = String::from_utf8_lossy(err.as_bytes());
             handler.fatal(format!("{}: {}",
                                   msg.as_slice(),
@@ -373,7 +373,7 @@ unsafe extern "C" fn diagnostic_handler(info: DiagnosticInfoRef, user: *mut c_vo
 
     match llvm::diagnostic::Diagnostic::unpack(info) {
         llvm::diagnostic::Optimization(opt) => {
-            let pass_name = CString::new(opt.pass_name, false);
+            let pass_name = CString::new(opt.pass_name);
             let pass_name = pass_name.as_str().expect("got a non-UTF8 pass name from LLVM");
             let enabled = match cgcx.remark {
                 AllPasses => true,
diff --git a/src/librustc/middle/trans/base.rs b/src/librustc/middle/trans/base.rs
index 5c9546bf212b8..ef6cab6a7d344 100644
--- a/src/librustc/middle/trans/base.rs
+++ b/src/librustc/middle/trans/base.rs
@@ -2988,7 +2988,7 @@ fn internalize_symbols(cx: &SharedCrateContext, reachable: &HashSet<String>) {
                     continue
                 }
 
-                let name = CString::new(llvm::LLVMGetValueName(val), false);
+                let name = CString::new(llvm::LLVMGetValueName(val));
                 declared.insert(name);
             }
         }
@@ -3004,7 +3004,7 @@ fn internalize_symbols(cx: &SharedCrateContext, reachable: &HashSet<String>) {
                     continue
                 }
 
-                let name = CString::new(llvm::LLVMGetValueName(val), false);
+                let name = CString::new(llvm::LLVMGetValueName(val));
                 if !declared.contains(&name) &&
                    !reachable.contains_equiv(name.as_str().unwrap()) {
                     llvm::SetLinkage(val, llvm::InternalLinkage);
diff --git a/src/librustc_llvm/lib.rs b/src/librustc_llvm/lib.rs
index 06456a91e03f3..178c737c3329f 100644
--- a/src/librustc_llvm/lib.rs
+++ b/src/librustc_llvm/lib.rs
@@ -1625,7 +1625,7 @@ extern {
 
     /** Returns a string describing the last error caused by an LLVMRust*
     call. */
-    pub fn LLVMRustGetLastError() -> *const c_char;
+    pub fn LLVMRustGetLastError() -> *mut c_char;
 
     /// Print the pass timings since static dtors aren't picking them up.
     pub fn LLVMRustPrintPassTimings();
diff --git a/src/librustrt/c_str.rs b/src/librustrt/c_str.rs
index b15cdb88b6783..e88d4bf3ab3c5 100644
--- a/src/librustrt/c_str.rs
+++ b/src/librustrt/c_str.rs
@@ -22,20 +22,6 @@ strings can validly contain a null-byte in the middle of the string (0 is a
 valid Unicode codepoint). This means that not all Rust strings can actually be
 translated to C strings.
 
-# Creation of a C string
-
-A C string is managed through the `CString` type defined in this module. It
-"owns" the internal buffer of characters and will automatically deallocate the
-buffer when the string is dropped. The `ToCStr` trait is implemented for `&str`
-and `&[u8]`, but the conversions can fail due to some of the limitations
-explained above.
-
-This also means that currently whenever a C string is created, an allocation
-must be performed to place the data elsewhere (the lifetime of the C string is
-not tied to the lifetime of the original string/data buffer). If C strings are
-heavily used in applications, then caching may be advisable to prevent
-unnecessary amounts of allocations.
-
 Be carefull to remember that the memory is managed by C allocator API and not
 by Rust allocator API.
 That means that the CString pointers should be freed with C allocator API
@@ -85,13 +71,17 @@ use core::slice;
 use core::str;
 use libc;
 
+enum CStringInner {
+  Owned(*mut libc::c_char),
+  NotOwned(*const libc::c_char),
+}
+
 /// The representation of a C String.
 ///
 /// This structure wraps a `*libc::c_char`, and will automatically free the
 /// memory it is pointing to when it goes out of scope.
 pub struct CString {
-    buf: *const libc::c_char,
-    owns_buffer_: bool,
+  inner: CStringInner,
 }
 
 impl Clone for CString {
@@ -102,19 +92,19 @@ impl Clone for CString {
         let len = self.len() + 1;
         let buf = unsafe { libc::malloc(len as libc::size_t) } as *mut libc::c_char;
         if buf.is_null() { ::alloc::oom() }
-        unsafe { ptr::copy_nonoverlapping_memory(buf, self.buf, len); }
-        CString { buf: buf as *const libc::c_char, owns_buffer_: true }
+        unsafe { ptr::copy_nonoverlapping_memory(buf, self.as_ptr(), len); }
+        CString { inner: Owned(buf) }
     }
 }
 
 impl PartialEq for CString {
     fn eq(&self, other: &CString) -> bool {
         // Check if the two strings share the same buffer
-        if self.buf as uint == other.buf as uint {
+        if self.as_ptr() as uint == other.as_ptr() as uint {
             true
         } else {
             unsafe {
-                libc::strcmp(self.buf, other.buf) == 0
+                libc::strcmp(self.as_ptr(), other.as_ptr()) == 0
             }
         }
     }
@@ -144,9 +134,20 @@ impl CString {
     ///# Failure
     ///
     /// Fails if `buf` is null
-    pub unsafe fn new(buf: *const libc::c_char, owns_buffer: bool) -> CString {
+    pub unsafe fn new(buf: *const libc::c_char) -> CString {
         assert!(!buf.is_null());
-        CString { buf: buf, owns_buffer_: owns_buffer }
+        CString { inner: NotOwned(buf) }
+    }
+
+    /// Like CString::new except that `buf` will be freed when the value goes
+    /// out of scope.
+    ///
+    ///# Failure
+    ///
+    /// Fails if `buf` is null
+    pub unsafe fn new_owned(buf: *mut libc::c_char) -> CString {
+        assert!(!buf.is_null());
+        CString { inner: Owned(buf) }
     }
 
     /// Return a pointer to the NUL-terminated string data.
@@ -179,8 +180,12 @@ impl CString {
     ///     }
     /// }
     /// ```
+    #[inline]
     pub fn as_ptr(&self) -> *const libc::c_char {
-        self.buf
+        match self.inner {
+            Owned(buf)    => buf as *const libc::c_char,
+            NotOwned(buf) => buf,
+        }
     }
 
     /// Return a mutable pointer to the NUL-terminated string data.
@@ -200,13 +205,20 @@ impl CString {
     /// // wrong (the CString will be freed, invalidating `p`)
     /// let p = foo.to_c_str().as_mut_ptr();
     /// ```
+    #[inline]
     pub fn as_mut_ptr(&mut self) -> *mut libc::c_char {
-        self.buf as *mut _
+        match self.inner {
+            Owned(buf)    => buf,
+            NotOwned(buf) => buf as *mut libc::c_char,
+        }
     }
 
     /// Returns whether or not the `CString` owns the buffer.
     pub fn owns_buffer(&self) -> bool {
-        self.owns_buffer_
+        match self.inner {
+            Owned(_)    => true,
+            NotOwned(_) => false,
+        }
     }
 
     /// Converts the CString into a `&[u8]` without copying.
@@ -214,7 +226,7 @@ impl CString {
     #[inline]
     pub fn as_bytes<'a>(&'a self) -> &'a [u8] {
         unsafe {
-            mem::transmute(Slice { data: self.buf, len: self.len() + 1 })
+            mem::transmute(Slice { data: self.as_ptr(), len: self.len() + 1 })
         }
     }
 
@@ -223,7 +235,7 @@ impl CString {
     #[inline]
     pub fn as_bytes_no_nul<'a>(&'a self) -> &'a [u8] {
         unsafe {
-            mem::transmute(Slice { data: self.buf, len: self.len() })
+            mem::transmute(Slice { data: self.as_ptr(), len: self.len() })
         }
     }
 
@@ -238,7 +250,7 @@ impl CString {
     /// Return a CString iterator.
     pub fn iter<'a>(&'a self) -> CChars<'a> {
         CChars {
-            ptr: self.buf,
+            ptr: self.as_ptr(),
             marker: marker::ContravariantLifetime,
         }
     }
@@ -255,15 +267,16 @@ impl CString {
     /// Prefer `.as_ptr()` when just retrieving a pointer to the
     /// string data, as that does not relinquish ownership.
     pub unsafe fn unwrap(mut self) -> *const libc::c_char {
-        self.owns_buffer_ = false;
-        self.buf
+        let ret = self.as_ptr();
+        self.inner = NotOwned(ret);
+        ret
     }
 
     /// Return the number of bytes in the CString (not including the NUL
     /// terminator).
     #[inline]
     pub fn len(&self) -> uint {
-        unsafe { libc::strlen(self.buf) as uint }
+        unsafe { libc::strlen(self.as_ptr()) as uint }
     }
 
     /// Returns if there are no bytes in this string
@@ -273,10 +286,11 @@ impl CString {
 
 impl Drop for CString {
     fn drop(&mut self) {
-        if self.owns_buffer_ {
-            unsafe {
-                libc::free(self.buf as *mut libc::c_void)
-            }
+        match self.inner {
+            Owned(buf)  => unsafe {
+                libc::free(buf as *mut libc::c_void)
+            },
+            _ => {},
         }
     }
 }
@@ -393,7 +407,7 @@ impl ToCStr for [u8] {
         ptr::copy_memory(buf, self.as_ptr(), self_len);
         *buf.offset(self_len as int) = 0;
 
-        CString::new(buf as *const libc::c_char, true)
+        CString::new_owned(buf as *mut libc::c_char)
     }
 
     fn with_c_str<T>(&self, f: |*const libc::c_char| -> T) -> T {
@@ -500,7 +514,7 @@ pub unsafe fn from_c_multistring(buf: *const libc::c_char,
     };
     while ((limited_count && ctr < limit) || !limited_count)
           && *(curr_ptr as *const libc::c_char) != 0 as libc::c_char {
-        let cstr = CString::new(curr_ptr as *const libc::c_char, false);
+        let cstr = CString::new(curr_ptr as *const libc::c_char);
         f(&cstr);
         curr_ptr += cstr.len() + 1;
         ctr += 1;
@@ -665,7 +679,7 @@ mod tests {
     #[test]
     #[should_fail]
     fn test_new_fail() {
-        let _c_str = unsafe { CString::new(ptr::null(), false) };
+        let _c_str = unsafe { CString::new(ptr::null()) };
     }
 
     #[test]
@@ -681,7 +695,7 @@ mod tests {
             let s = "test".to_string();
             let c = s.to_c_str();
             // give the closure a non-owned CString
-            let mut c_ = unsafe { CString::new(c.as_ptr(), false) };
+            let mut c_ = unsafe { CString::new(c.as_ptr()) };
             f(&c_);
             // muck with the buffer for later printing
             unsafe { *c_.as_mut_ptr() = 'X' as libc::c_char }
diff --git a/src/libstd/dynamic_lib.rs b/src/libstd/dynamic_lib.rs
index 4c133fc739739..91e42a55323c2 100644
--- a/src/libstd/dynamic_lib.rs
+++ b/src/libstd/dynamic_lib.rs
@@ -242,7 +242,7 @@ pub mod dl {
             let ret = if ptr::null() == last_error {
                 Ok(result)
             } else {
-                Err(String::from_str(CString::new(last_error, false).as_str()
+                Err(String::from_str(CString::new(last_error).as_str()
                     .unwrap()))
             };
 
diff --git a/src/libstd/os.rs b/src/libstd/os.rs
index 9846f7b653e2b..face785be5f34 100644
--- a/src/libstd/os.rs
+++ b/src/libstd/os.rs
@@ -100,7 +100,7 @@ pub fn getcwd() -> Path {
         if libc::getcwd(buf.as_mut_ptr(), buf.len() as libc::size_t).is_null() {
             panic!()
         }
-        Path::new(CString::new(buf.as_ptr(), false))
+        Path::new(CString::new(buf.as_ptr()))
     }
 }
 
@@ -288,7 +288,7 @@ pub fn env_as_bytes() -> Vec<(Vec<u8>,Vec<u8>)> {
             let mut result = Vec::new();
             while *environ != 0 as *const _ {
                 let env_pair =
-                    CString::new(*environ, false).as_bytes_no_nul().to_vec();
+                    CString::new(*environ).as_bytes_no_nul().to_vec();
                 result.push(env_pair);
                 environ = environ.offset(1);
             }
@@ -355,7 +355,7 @@ pub fn getenv_as_bytes(n: &str) -> Option<Vec<u8>> {
             if s.is_null() {
                 None
             } else {
-                Some(CString::new(s as *const i8, false).as_bytes_no_nul().to_vec())
+                Some(CString::new(s as *const i8).as_bytes_no_nul().to_vec())
             }
         })
     }
@@ -1103,7 +1103,7 @@ unsafe fn load_argc_and_argv(argc: int,
     use c_str::CString;
 
     Vec::from_fn(argc as uint, |i| {
-        CString::new(*argv.offset(i as int), false).as_bytes_no_nul().to_vec()
+        CString::new(*argv.offset(i as int)).as_bytes_no_nul().to_vec()
     })
 }
 
@@ -1170,7 +1170,7 @@ fn real_args_as_bytes() -> Vec<Vec<u8>> {
             let tmp = objc_msgSend(args, objectAtSel, i);
             let utf_c_str: *const libc::c_char =
                 mem::transmute(objc_msgSend(tmp, utf8Sel));
-            let s = CString::new(utf_c_str, false);
+            let s = CString::new(utf_c_str);
             res.push(s.as_bytes_no_nul().to_vec())
         }
     }
diff --git a/src/libstd/rt/backtrace.rs b/src/libstd/rt/backtrace.rs
index 5d7aa0509c5d8..32733f19f6cfe 100644
--- a/src/libstd/rt/backtrace.rs
+++ b/src/libstd/rt/backtrace.rs
@@ -382,7 +382,7 @@ mod imp {
             output(w, idx,addr, None)
         } else {
             output(w, idx, addr, Some(unsafe {
-                CString::new(info.dli_sname, false)
+                CString::new(info.dli_sname)
             }))
         }
     }
@@ -516,7 +516,7 @@ mod imp {
         if ret == 0 || data.is_null() {
             output(w, idx, addr, None)
         } else {
-            output(w, idx, addr, Some(unsafe { CString::new(data, false) }))
+            output(w, idx, addr, Some(unsafe { CString::new(data) }))
         }
     }
 
@@ -990,7 +990,7 @@ mod imp {
 
             if ret == libc::TRUE {
                 try!(write!(w, " - "));
-                let cstr = unsafe { CString::new(info.Name.as_ptr(), false) };
+                let cstr = unsafe { CString::new(info.Name.as_ptr()) };
                 let bytes = cstr.as_bytes();
                 match cstr.as_str() {
                     Some(s) => try!(super::demangle(w, s)),
diff --git a/src/test/run-pass/unix-process-spawn-errno.rs b/src/test/run-pass/unix-process-spawn-errno.rs
index b2ef1a044db80..7497d6c2eb0ab 100644
--- a/src/test/run-pass/unix-process-spawn-errno.rs
+++ b/src/test/run-pass/unix-process-spawn-errno.rs
@@ -24,7 +24,7 @@ use rustrt::c_str;
 macro_rules! c_string {
     ($s:expr) => { {
         let ptr = concat!($s, "\0").as_ptr() as *const i8;
-        unsafe { &c_str::CString::new(ptr, false) }
+        unsafe { &c_str::CString::new(ptr) }
     } }
 }
 
diff --git a/src/test/run-pass/variadic-ffi.rs b/src/test/run-pass/variadic-ffi.rs
index 570b881650ae8..9c911ad7ffbef 100644
--- a/src/test/run-pass/variadic-ffi.rs
+++ b/src/test/run-pass/variadic-ffi.rs
@@ -21,7 +21,7 @@ extern {
 unsafe fn check<T>(expected: &str, f: |*mut c_char| -> T) {
     let mut x = [0i8, ..50];
     f(&mut x[0] as *mut c_char);
-    let res = CString::new(&x[0], false);
+    let res = CString::new(&x[0]);
     assert_eq!(expected, res.as_str().unwrap());
 }