diff --git a/doc/guide-ffi.md b/doc/guide-ffi.md
index 236da56588e9..217eab527582 100644
--- a/doc/guide-ffi.md
+++ b/doc/guide-ffi.md
@@ -230,7 +230,7 @@ impl<T: Send> Drop for Unique<T> {
             // We need to move the object out of the box, so that
             // the destructor is called (at the end of this scope.)
             ptr::replace_ptr(self.ptr, x);
-            free(self.ptr as *c_void)
+            free(self.ptr as *mut c_void)
         }
     }
 }
diff --git a/src/libextra/c_vec.rs b/src/libextra/c_vec.rs
index fc2caa13584d..35a6ccaa7083 100644
--- a/src/libextra/c_vec.rs
+++ b/src/libextra/c_vec.rs
@@ -172,7 +172,7 @@ mod tests {
             let mem = malloc_raw(n);
 
             CVec::new_with_dtor(mem as *mut u8, n,
-                proc() { libc::free(mem as *c_void); })
+                proc() { libc::free(mem as *mut c_void); })
         }
     }
 
diff --git a/src/libextra/flate.rs b/src/libextra/flate.rs
index 1153c3a6ef30..faceb17af476 100644
--- a/src/libextra/flate.rs
+++ b/src/libextra/flate.rs
@@ -53,7 +53,7 @@ fn deflate_bytes_internal(bytes: &[u8], flags: c_int) -> ~[u8] {
         assert!(res as int != 0);
             let out = vec::raw::from_buf_raw(res as *u8,
                                              outsz as uint);
-        libc::free(res);
+        libc::free(res as *mut c_void);
         out
     }
 }
@@ -76,7 +76,7 @@ fn inflate_bytes_internal(bytes: &[u8], flags: c_int) -> ~[u8] {
         assert!(res as int != 0);
         let out = vec::raw::from_buf_raw(res as *u8,
                                          outsz as uint);
-        libc::free(res);
+        libc::free(res as *mut c_void);
         out
     }
 }
diff --git a/src/libnative/io/file.rs b/src/libnative/io/file.rs
index af6ed51729ef..af06533d44bd 100644
--- a/src/libnative/io/file.rs
+++ b/src/libnative/io/file.rs
@@ -548,13 +548,13 @@ pub fn readdir(p: &CString) -> IoResult<~[Path]> {
             let p = Path::new(p);
             let star = p.join("*");
             as_utf16_p(star.as_str().unwrap(), |path_ptr| {
-                let wfd_ptr = malloc_raw(rust_list_dir_wfd_size() as uint) as *c_void;
+                let wfd_ptr = malloc_raw(rust_list_dir_wfd_size() as uint);
                 let find_handle = FindFirstFileW(path_ptr, wfd_ptr as HANDLE);
                 if find_handle as libc::c_int != INVALID_HANDLE_VALUE {
                     let mut paths = ~[];
                     let mut more_files = 1 as libc::c_int;
                     while more_files != 0 {
-                        let fp_buf = rust_list_dir_wfd_fp_buf(wfd_ptr);
+                        let fp_buf = rust_list_dir_wfd_fp_buf(wfd_ptr as *c_void);
                         if fp_buf as uint == 0 {
                             fail!("os::list_dir() failure: got null ptr from wfd");
                         }
@@ -567,7 +567,7 @@ pub fn readdir(p: &CString) -> IoResult<~[Path]> {
                         more_files = FindNextFileW(find_handle, wfd_ptr as HANDLE);
                     }
                     FindClose(find_handle);
-                    free(wfd_ptr);
+                    free(wfd_ptr as *mut c_void);
                     Ok(paths)
                 } else {
                     Err(super::last_error())
diff --git a/src/librustc/lib/llvm.rs b/src/librustc/lib/llvm.rs
index c259fa6a6183..3693b00951bc 100644
--- a/src/librustc/lib/llvm.rs
+++ b/src/librustc/lib/llvm.rs
@@ -1836,7 +1836,7 @@ impl TypeNames {
         unsafe {
             let s = llvm::LLVMTypeToString(ty.to_ref());
             let ret = from_c_str(s);
-            free(s as *c_void);
+            free(s as *mut c_void);
             ret
         }
     }
@@ -1850,7 +1850,7 @@ impl TypeNames {
         unsafe {
             let s = llvm::LLVMValueToString(val);
             let ret = from_c_str(s);
-            free(s as *c_void);
+            free(s as *mut c_void);
             ret
         }
     }
diff --git a/src/librustuv/uvll.rs b/src/librustuv/uvll.rs
index 189a820cd3ee..0a6e23e99564 100644
--- a/src/librustuv/uvll.rs
+++ b/src/librustuv/uvll.rs
@@ -373,7 +373,7 @@ pub unsafe fn malloc_handle(handle: uv_handle_type) -> *c_void {
 }
 
 pub unsafe fn free_handle(v: *c_void) {
-    free(v)
+    free(v as *mut c_void)
 }
 
 pub unsafe fn malloc_req(req: uv_req_type) -> *c_void {
@@ -383,7 +383,7 @@ pub unsafe fn malloc_req(req: uv_req_type) -> *c_void {
 }
 
 pub unsafe fn free_req(v: *c_void) {
-    free(v)
+    free(v as *mut c_void)
 }
 
 #[test]
diff --git a/src/libstd/c_str.rs b/src/libstd/c_str.rs
index c735e3250682..22e93e581944 100644
--- a/src/libstd/c_str.rs
+++ b/src/libstd/c_str.rs
@@ -183,7 +183,7 @@ impl Drop for CString {
     fn drop(&mut self) {
         if self.owns_buffer_ {
             unsafe {
-                libc::free(self.buf as *libc::c_void)
+                libc::free(self.buf as *mut libc::c_void)
             }
         }
     }
@@ -459,7 +459,7 @@ mod tests {
     #[test]
     fn test_unwrap() {
         let c_str = "hello".to_c_str();
-        unsafe { libc::free(c_str.unwrap() as *libc::c_void) }
+        unsafe { libc::free(c_str.unwrap() as *mut libc::c_void) }
     }
 
     #[test]
diff --git a/src/libstd/libc.rs b/src/libstd/libc.rs
index 77ac226a7f16..a2aa182216a6 100644
--- a/src/libstd/libc.rs
+++ b/src/libstd/libc.rs
@@ -3225,7 +3225,7 @@ pub mod funcs {
                 pub fn calloc(nobj: size_t, size: size_t) -> *c_void;
                 pub fn malloc(size: size_t) -> *mut c_void;
                 pub fn realloc(p: *mut c_void, size: size_t) -> *mut c_void;
-                pub fn free(p: *c_void);
+                pub fn free(p: *mut c_void);
                 pub fn exit(status: c_int) -> !;
                 // Omitted: atexit.
                 pub fn system(s: *c_char) -> c_int;
diff --git a/src/libstd/rt/global_heap.rs b/src/libstd/rt/global_heap.rs
index 54442cedb683..ead78ce41ef9 100644
--- a/src/libstd/rt/global_heap.rs
+++ b/src/libstd/rt/global_heap.rs
@@ -52,7 +52,7 @@ pub unsafe fn realloc_raw(ptr: *mut u8, size: uint) -> *mut u8 {
     // `realloc(ptr, 0)` may allocate, but it may also return a null pointer
     // http://pubs.opengroup.org/onlinepubs/9699919799/functions/realloc.html
     if size == 0 {
-        free(ptr as *c_void);
+        free(ptr);
         mut_null()
     } else {
         let p = realloc(ptr as *mut c_void, size as size_t);
@@ -107,7 +107,7 @@ pub unsafe fn exchange_free_(ptr: *u8) {
 
 #[inline]
 pub unsafe fn exchange_free(ptr: *u8) {
-    free(ptr as *c_void);
+    free(ptr as *mut c_void);
 }
 
 #[cfg(test)]
diff --git a/src/libstd/sync/deque.rs b/src/libstd/sync/deque.rs
index e99e9ef09403..e740862fddfb 100644
--- a/src/libstd/sync/deque.rs
+++ b/src/libstd/sync/deque.rs
@@ -389,7 +389,7 @@ impl<T: Send> Buffer<T> {
 impl<T: Send> Drop for Buffer<T> {
     fn drop(&mut self) {
         // It is assumed that all buffers are empty on drop.
-        unsafe { libc::free(self.storage as *libc::c_void) }
+        unsafe { libc::free(self.storage as *mut libc::c_void) }
     }
 }
 
diff --git a/src/libstd/unstable/mutex.rs b/src/libstd/unstable/mutex.rs
index ff38a8c01993..69c6204cc323 100644
--- a/src/libstd/unstable/mutex.rs
+++ b/src/libstd/unstable/mutex.rs
@@ -173,49 +173,49 @@ mod imp {
     type pthread_condattr_t = libc::c_void;
 
     pub unsafe fn init_lock() -> uint {
-        let block = malloc_raw(rust_pthread_mutex_t_size() as uint) as *pthread_mutex_t;
+        let block = malloc_raw(rust_pthread_mutex_t_size() as uint) as *mut pthread_mutex_t;
         let n = pthread_mutex_init(block, ptr::null());
         assert_eq!(n, 0);
         return block as uint;
     }
 
     pub unsafe fn init_cond() -> uint {
-        let block = malloc_raw(rust_pthread_cond_t_size() as uint) as *pthread_cond_t;
+        let block = malloc_raw(rust_pthread_cond_t_size() as uint) as *mut pthread_cond_t;
         let n = pthread_cond_init(block, ptr::null());
         assert_eq!(n, 0);
         return block as uint;
     }
 
     pub unsafe fn free_lock(h: uint) {
-        let block = h as *libc::c_void;
+        let block = h as *mut libc::c_void;
         assert_eq!(pthread_mutex_destroy(block), 0);
         libc::free(block);
     }
 
     pub unsafe fn free_cond(h: uint) {
-        let block = h as *pthread_cond_t;
+        let block = h as *mut pthread_cond_t;
         assert_eq!(pthread_cond_destroy(block), 0);
         libc::free(block);
     }
 
     pub unsafe fn lock(l: uint) {
-        assert_eq!(pthread_mutex_lock(l as *pthread_mutex_t), 0);
+        assert_eq!(pthread_mutex_lock(l as *mut pthread_mutex_t), 0);
     }
 
     pub unsafe fn trylock(l: uint) -> bool {
-        pthread_mutex_trylock(l as *pthread_mutex_t) == 0
+        pthread_mutex_trylock(l as *mut pthread_mutex_t) == 0
     }
 
     pub unsafe fn unlock(l: uint) {
-        assert_eq!(pthread_mutex_unlock(l as *pthread_mutex_t), 0);
+        assert_eq!(pthread_mutex_unlock(l as *mut pthread_mutex_t), 0);
     }
 
     pub unsafe fn wait(cond: uint, m: uint) {
-        assert_eq!(pthread_cond_wait(cond as *pthread_cond_t, m as *pthread_mutex_t), 0);
+        assert_eq!(pthread_cond_wait(cond as *mut pthread_cond_t, m as *mut pthread_mutex_t), 0);
     }
 
     pub unsafe fn signal(cond: uint) {
-        assert_eq!(pthread_cond_signal(cond as *pthread_cond_t), 0);
+        assert_eq!(pthread_cond_signal(cond as *mut pthread_cond_t), 0);
     }
 
     extern {
@@ -224,19 +224,19 @@ mod imp {
     }
 
     extern {
-        fn pthread_mutex_init(lock: *pthread_mutex_t,
+        fn pthread_mutex_init(lock: *mut pthread_mutex_t,
                               attr: *pthread_mutexattr_t) -> libc::c_int;
-        fn pthread_mutex_destroy(lock: *pthread_mutex_t) -> libc::c_int;
-        fn pthread_cond_init(cond: *pthread_cond_t,
+        fn pthread_mutex_destroy(lock: *mut pthread_mutex_t) -> libc::c_int;
+        fn pthread_cond_init(cond: *mut pthread_cond_t,
                               attr: *pthread_condattr_t) -> libc::c_int;
-        fn pthread_cond_destroy(cond: *pthread_cond_t) -> libc::c_int;
-        fn pthread_mutex_lock(lock: *pthread_mutex_t) -> libc::c_int;
-        fn pthread_mutex_trylock(lock: *pthread_mutex_t) -> libc::c_int;
-        fn pthread_mutex_unlock(lock: *pthread_mutex_t) -> libc::c_int;
+        fn pthread_cond_destroy(cond: *mut pthread_cond_t) -> libc::c_int;
+        fn pthread_mutex_lock(lock: *mut pthread_mutex_t) -> libc::c_int;
+        fn pthread_mutex_trylock(lock: *mut pthread_mutex_t) -> libc::c_int;
+        fn pthread_mutex_unlock(lock: *mut pthread_mutex_t) -> libc::c_int;
 
-        fn pthread_cond_wait(cond: *pthread_cond_t,
-                             lock: *pthread_mutex_t) -> libc::c_int;
-        fn pthread_cond_signal(cond: *pthread_cond_t) -> libc::c_int;
+        fn pthread_cond_wait(cond: *mut pthread_cond_t,
+                             lock: *mut pthread_mutex_t) -> libc::c_int;
+        fn pthread_cond_signal(cond: *mut pthread_cond_t) -> libc::c_int;
     }
 }
 
@@ -263,7 +263,7 @@ mod imp {
 
     pub unsafe fn free_lock(h: uint) {
         DeleteCriticalSection(h as LPCRITICAL_SECTION);
-        libc::free(h as *c_void);
+        libc::free(h as *mut c_void);
     }
 
     pub unsafe fn free_cond(h: uint) {