diff --git a/src/libgreen/stack.rs b/src/libgreen/stack.rs
index 2e385f75e1d3e..526ce66b1ead8 100644
--- a/src/libgreen/stack.rs
+++ b/src/libgreen/stack.rs
@@ -96,7 +96,7 @@ fn protect_last_page(stack: &MemoryMap) -> bool {
         // This may seem backwards: the start of the segment is the last page?
         // Yes! The stack grows from higher addresses (the end of the allocated
         // block) to lower addresses (the start of the allocated block).
-        let last_page = stack.data as *libc::c_void;
+        let last_page = stack.data as *mut libc::c_void;
         libc::mprotect(last_page, page_size() as libc::size_t,
                        libc::PROT_NONE) != -1
     }
diff --git a/src/liblibc/lib.rs b/src/liblibc/lib.rs
index 05d9988a13965..2a464d82fd979 100644
--- a/src/liblibc/lib.rs
+++ b/src/liblibc/lib.rs
@@ -2057,7 +2057,7 @@ pub mod consts {
             pub static MAP_FIXED : c_int = 0x0010;
             pub static MAP_ANON : c_int = 0x0020;
 
-            pub static MAP_FAILED : *c_void = -1 as *c_void;
+            pub static MAP_FAILED : *mut c_void = -1 as *mut c_void;
 
             pub static MCL_CURRENT : c_int = 0x0001;
             pub static MCL_FUTURE : c_int = 0x0002;
@@ -2268,7 +2268,7 @@ pub mod consts {
             pub static MAP_FIXED : c_int = 0x0010;
             pub static MAP_ANON : c_int = 0x0800;
 
-            pub static MAP_FAILED : *c_void = -1 as *c_void;
+            pub static MAP_FAILED : *mut c_void = -1 as *mut c_void;
 
             pub static MCL_CURRENT : c_int = 0x0001;
             pub static MCL_FUTURE : c_int = 0x0002;
@@ -2804,7 +2804,7 @@ pub mod consts {
             pub static MAP_FIXED : c_int = 0x0010;
             pub static MAP_ANON : c_int = 0x1000;
 
-            pub static MAP_FAILED : *c_void = -1 as *c_void;
+            pub static MAP_FAILED : *mut c_void = -1 as *mut c_void;
 
             pub static MCL_CURRENT : c_int = 0x0001;
             pub static MCL_FUTURE : c_int = 0x0002;
@@ -3192,7 +3192,7 @@ pub mod consts {
             pub static MAP_FIXED : c_int = 0x0010;
             pub static MAP_ANON : c_int = 0x1000;
 
-            pub static MAP_FAILED : *c_void = -1 as *c_void;
+            pub static MAP_FAILED : *mut c_void = -1 as *mut c_void;
 
             pub static MCL_CURRENT : c_int = 0x0001;
             pub static MCL_FUTURE : c_int = 0x0002;
@@ -3951,19 +3951,19 @@ pub mod funcs {
                 pub fn mlockall(flags: c_int) -> c_int;
                 pub fn munlockall() -> c_int;
 
-                pub fn mmap(addr: *c_void,
+                pub fn mmap(addr: *mut c_void,
                             len: size_t,
                             prot: c_int,
                             flags: c_int,
                             fd: c_int,
                             offset: off_t)
                             -> *mut c_void;
-                pub fn munmap(addr: *c_void, len: size_t) -> c_int;
+                pub fn munmap(addr: *mut c_void, len: size_t) -> c_int;
 
-                pub fn mprotect(addr: *c_void, len: size_t, prot: c_int)
+                pub fn mprotect(addr: *mut c_void, len: size_t, prot: c_int)
                                 -> c_int;
 
-                pub fn msync(addr: *c_void, len: size_t, flags: c_int)
+                pub fn msync(addr: *mut c_void, len: size_t, flags: c_int)
                              -> c_int;
                 pub fn shm_open(name: *c_char, oflag: c_int, mode: mode_t)
                                 -> c_int;
@@ -4208,9 +4208,9 @@ pub mod funcs {
 
         extern {
             pub fn getdtablesize() -> c_int;
-            pub fn madvise(addr: *c_void, len: size_t, advice: c_int)
+            pub fn madvise(addr: *mut c_void, len: size_t, advice: c_int)
                            -> c_int;
-            pub fn mincore(addr: *c_void, len: size_t, vec: *c_uchar)
+            pub fn mincore(addr: *mut c_void, len: size_t, vec: *mut c_uchar)
                            -> c_int;
         }
     }
diff --git a/src/libstd/os.rs b/src/libstd/os.rs
index dfbf61cc890b7..4d58d4674bf9a 100644
--- a/src/libstd/os.rs
+++ b/src/libstd/os.rs
@@ -1338,7 +1338,6 @@ impl MemoryMap {
     /// `ErrZeroLength`.
     pub fn new(min_len: uint, options: &[MapOption]) -> Result<MemoryMap, MapError> {
         use libc::off_t;
-        use cmp::Equiv;
 
         if min_len == 0 {
             return Err(ErrZeroLength)
@@ -1371,10 +1370,10 @@ impl MemoryMap {
         if fd == -1 && !custom_flags { flags |= libc::MAP_ANON; }
 
         let r = unsafe {
-            libc::mmap(addr as *c_void, len as libc::size_t, prot, flags, fd,
-                       offset)
+            libc::mmap(addr as *mut c_void, len as libc::size_t, prot, flags,
+                       fd, offset)
         };
-        if r.equiv(&libc::MAP_FAILED) {
+        if r == libc::MAP_FAILED {
             Err(match errno() as c_int {
                 libc::EACCES => ErrFdNotAvail,
                 libc::EBADF => ErrInvalidFd,
@@ -1410,8 +1409,8 @@ impl Drop for MemoryMap {
         if self.len == 0 { /* workaround for dummy_stack */ return; }
 
         unsafe {
-            // FIXME: what to do if this fails?
-            let _ = libc::munmap(self.data as *c_void, self.len as libc::size_t);
+            // `munmap` only fails due to logic errors
+            libc::munmap(self.data as *mut c_void, self.len as libc::size_t);
         }
     }
 }