diff --git a/src/bootstrap/cache.rs b/src/bootstrap/cache.rs
index c27493158826c..f9659fc25688a 100644
--- a/src/bootstrap/cache.rs
+++ b/src/bootstrap/cache.rs
@@ -17,7 +17,6 @@ use std::ffi::OsStr;
 use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::marker::PhantomData;
-use std::mem;
 use std::ops::Deref;
 use std::path::{Path, PathBuf};
 use std::sync::Mutex;
@@ -114,7 +113,8 @@ impl Deref for Interned<String> {
     type Target = str;
     fn deref(&self) -> &'static str {
         let l = INTERNER.strs.lock().unwrap();
-        unsafe { mem::transmute::<&str, &'static str>(l.get(*self)) }
+        let s: &str = l.get(*self).as_ref();
+        unsafe { &*(s as *const _) }
     }
 }
 
@@ -122,35 +122,40 @@ impl Deref for Interned<PathBuf> {
     type Target = Path;
     fn deref(&self) -> &'static Path {
         let l = INTERNER.paths.lock().unwrap();
-        unsafe { mem::transmute::<&Path, &'static Path>(l.get(*self)) }
+        let p: &Path = l.get(*self).as_ref();
+        unsafe { &*(p as *const _) }
     }
 }
 
 impl AsRef<Path> for Interned<PathBuf> {
     fn as_ref(&self) -> &'static Path {
         let l = INTERNER.paths.lock().unwrap();
-        unsafe { mem::transmute::<&Path, &'static Path>(l.get(*self)) }
+        let p: &Path = l.get(*self).as_ref();
+        unsafe { &*(p as *const _) }
     }
 }
 
 impl AsRef<Path> for Interned<String> {
     fn as_ref(&self) -> &'static Path {
         let l = INTERNER.strs.lock().unwrap();
-        unsafe { mem::transmute::<&Path, &'static Path>(l.get(*self).as_ref()) }
+        let p: &Path = l.get(*self).as_ref();
+        unsafe { &*(p as *const _) }
     }
 }
 
 impl AsRef<OsStr> for Interned<PathBuf> {
     fn as_ref(&self) -> &'static OsStr {
         let l = INTERNER.paths.lock().unwrap();
-        unsafe { mem::transmute::<&OsStr, &'static OsStr>(l.get(*self).as_ref()) }
+        let s: &OsStr = l.get(*self).as_ref();
+        unsafe { &*(s as *const _) }
     }
 }
 
 impl AsRef<OsStr> for Interned<String> {
     fn as_ref(&self) -> &'static OsStr {
         let l = INTERNER.strs.lock().unwrap();
-        unsafe { mem::transmute::<&OsStr, &'static OsStr>(l.get(*self).as_ref()) }
+        let s: &OsStr = l.get(*self).as_ref();
+        unsafe { &*(s as *const _) }
     }
 }
 
diff --git a/src/librustc/ty/mod.rs b/src/librustc/ty/mod.rs
index e5f6ac8853067..fe4f01a8011b2 100644
--- a/src/librustc/ty/mod.rs
+++ b/src/librustc/ty/mod.rs
@@ -46,7 +46,6 @@ use std::ops::Deref;
 use std::rc::Rc;
 use std::slice;
 use std::vec::IntoIter;
-use std::mem;
 use syntax::ast::{self, DUMMY_NODE_ID, Name, Ident, NodeId};
 use syntax::attr;
 use syntax::ext::hygiene::{Mark, SyntaxContext};
@@ -592,7 +591,8 @@ impl<'tcx> serialize::UseSpecializedDecodable for &'tcx Slice<Ty<'tcx>> {}
 impl<T> Slice<T> {
     pub fn empty<'a>() -> &'a Slice<T> {
         unsafe {
-            mem::transmute(slice::from_raw_parts(0x1 as *const T, 0))
+            let slice = slice::from_raw_parts(0x1 as *const T, 0);
+            &*(slice as *const [T] as *const Slice<T>)
         }
     }
 }
diff --git a/src/librustc_data_structures/blake2b.rs b/src/librustc_data_structures/blake2b.rs
index 6b8bf8df0d33f..abecf24a5614d 100644
--- a/src/librustc_data_structures/blake2b.rs
+++ b/src/librustc_data_structures/blake2b.rs
@@ -128,8 +128,7 @@ fn blake2b_compress(ctx: &mut Blake2bCtx, last: bool) {
         // before it's overwritten.
 
         let m: &mut [u64; 16] = unsafe {
-            let b: &mut [u8; 128] = &mut ctx.b;
-            ::std::mem::transmute(b)
+            &mut *(&mut ctx.b as *mut [u8; 128] as *mut [u64; 16])
         };
 
         if cfg!(target_endian = "big") {
diff --git a/src/librustc_data_structures/stable_hasher.rs b/src/librustc_data_structures/stable_hasher.rs
index d82b712b5b14b..c325a3cdd17de 100644
--- a/src/librustc_data_structures/stable_hasher.rs
+++ b/src/librustc_data_structures/stable_hasher.rs
@@ -241,10 +241,7 @@ impl<CTX> HashStable<CTX> for f32 {
     fn hash_stable<W: StableHasherResult>(&self,
                                           ctx: &mut CTX,
                                           hasher: &mut StableHasher<W>) {
-        let val: u32 = unsafe {
-            ::std::mem::transmute(*self)
-        };
-        val.hash_stable(ctx, hasher);
+        self.to_bits().hash_stable(ctx, hasher);
     }
 }
 
@@ -252,10 +249,7 @@ impl<CTX> HashStable<CTX> for f64 {
     fn hash_stable<W: StableHasherResult>(&self,
                                           ctx: &mut CTX,
                                           hasher: &mut StableHasher<W>) {
-        let val: u64 = unsafe {
-            ::std::mem::transmute(*self)
-        };
-        val.hash_stable(ctx, hasher);
+        self.to_bits().hash_stable(ctx, hasher);
     }
 }
 
diff --git a/src/librustc_trans/type_.rs b/src/librustc_trans/type_.rs
index 6cbe175d4d8d5..6597e0b76fe15 100644
--- a/src/librustc_trans/type_.rs
+++ b/src/librustc_trans/type_.rs
@@ -21,7 +21,6 @@ use rustc::ty::layout::{self, Align, Size};
 
 use std::ffi::CString;
 use std::fmt;
-use std::mem;
 use std::ptr;
 
 use libc::c_uint;
@@ -59,7 +58,7 @@ impl Type {
     }
 
     pub fn to_ref_slice(slice: &[Type]) -> &[TypeRef] {
-        unsafe { mem::transmute(slice) }
+        unsafe { &*(slice as *const [Type] as *const [TypeRef]) }
     }
 
     pub fn void(ccx: &CrateContext) -> Type {
diff --git a/src/libstd/error.rs b/src/libstd/error.rs
index eb5022ad5776a..cc48be83874f5 100644
--- a/src/libstd/error.rs
+++ b/src/libstd/error.rs
@@ -59,7 +59,6 @@ use char;
 use convert;
 use core::array;
 use fmt::{self, Debug, Display};
-use mem::transmute;
 use num;
 use str;
 use string;
@@ -491,11 +490,11 @@ impl Error + Send {
     #[stable(feature = "error_downcast", since = "1.3.0")]
     /// Attempt to downcast the box to a concrete type.
     pub fn downcast<T: Error + 'static>(self: Box<Self>)
-                                        -> Result<Box<T>, Box<Error + Send>> {
+                                        -> Result<Box<T>, Box<Self>> {
         let err: Box<Error> = self;
         <Error>::downcast(err).map_err(|s| unsafe {
             // reapply the Send marker
-            transmute::<Box<Error>, Box<Error + Send>>(s)
+            Box::from_raw(Box::into_raw(s) as *mut Self)
         })
     }
 }
@@ -509,7 +508,7 @@ impl Error + Send + Sync {
         let err: Box<Error> = self;
         <Error>::downcast(err).map_err(|s| unsafe {
             // reapply the Send+Sync marker
-            transmute::<Box<Error>, Box<Error + Send + Sync>>(s)
+            Box::from_raw(Box::into_raw(s) as *mut Self)
         })
     }
 }
diff --git a/src/libstd/sys/redox/args.rs b/src/libstd/sys/redox/args.rs
index 59ae2a74a6ddd..afda25a367cdd 100644
--- a/src/libstd/sys/redox/args.rs
+++ b/src/libstd/sys/redox/args.rs
@@ -57,7 +57,6 @@ impl DoubleEndedIterator for Args {
 
 mod imp {
     use os::unix::prelude::*;
-    use mem;
     use ffi::{CStr, OsString};
     use marker::PhantomData;
     use libc;
@@ -105,7 +104,7 @@ mod imp {
     }
 
     fn get_global_ptr() -> *mut Option<Box<Vec<Vec<u8>>>> {
-        unsafe { mem::transmute(&GLOBAL_ARGS_PTR) }
+        unsafe { &mut GLOBAL_ARGS_PTR as *mut _ as *mut _ }
     }
 
 }
diff --git a/src/libstd/sys/redox/ext/ffi.rs b/src/libstd/sys/redox/ext/ffi.rs
index d59b4fc0b70b8..06968bc4871ab 100644
--- a/src/libstd/sys/redox/ext/ffi.rs
+++ b/src/libstd/sys/redox/ext/ffi.rs
@@ -13,7 +13,6 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use ffi::{OsStr, OsString};
-use mem;
 use sys::os_str::Buf;
 use sys_common::{FromInner, IntoInner, AsInner};
 
@@ -53,7 +52,7 @@ pub trait OsStrExt {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl OsStrExt for OsStr {
     fn from_bytes(slice: &[u8]) -> &OsStr {
-        unsafe { mem::transmute(slice) }
+        unsafe { &*(slice as *const [u8] as *const OsStr) }
     }
     fn as_bytes(&self) -> &[u8] {
         &self.as_inner().inner
diff --git a/src/libstd/sys/redox/os_str.rs b/src/libstd/sys/redox/os_str.rs
index 655bfdb916707..b00e2f56aa5e7 100644
--- a/src/libstd/sys/redox/os_str.rs
+++ b/src/libstd/sys/redox/os_str.rs
@@ -14,7 +14,6 @@
 use borrow::Cow;
 use fmt;
 use str;
-use mem;
 use rc::Rc;
 use sync::Arc;
 use sys_common::{AsInner, IntoInner};
@@ -105,7 +104,7 @@ impl Buf {
     }
 
     pub fn as_slice(&self) -> &Slice {
-        unsafe { mem::transmute(&*self.inner) }
+        unsafe { &*(&*self.inner as *const [u8] as *const Slice) }
     }
 
     pub fn into_string(self) -> Result<String, Buf> {
@@ -118,12 +117,13 @@ impl Buf {
 
     #[inline]
     pub fn into_box(self) -> Box<Slice> {
-        unsafe { mem::transmute(self.inner.into_boxed_slice()) }
+        let boxed = self.inner.into_boxed_slice();
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     #[inline]
     pub fn from_box(boxed: Box<Slice>) -> Buf {
-        let inner: Box<[u8]> = unsafe { mem::transmute(boxed) };
+        let inner = unsafe { Box::from_raw(Box::into_raw(boxed) as *mut [u8]) };
         Buf { inner: inner.into_vec() }
     }
 
@@ -140,7 +140,7 @@ impl Buf {
 
 impl Slice {
     fn from_u8_slice(s: &[u8]) -> &Slice {
-        unsafe { mem::transmute(s) }
+        unsafe { &*(s as *const [u8] as *const Slice) }
     }
 
     pub fn from_str(s: &str) -> &Slice {
@@ -162,12 +162,12 @@ impl Slice {
     #[inline]
     pub fn into_box(&self) -> Box<Slice> {
         let boxed: Box<[u8]> = self.inner.into();
-        unsafe { mem::transmute(boxed) }
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     pub fn empty_box() -> Box<Slice> {
         let boxed: Box<[u8]> = Default::default();
-        unsafe { mem::transmute(boxed) }
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     #[inline]
diff --git a/src/libstd/sys/unix/os_str.rs b/src/libstd/sys/unix/os_str.rs
index e034938799866..19a7d341d479e 100644
--- a/src/libstd/sys/unix/os_str.rs
+++ b/src/libstd/sys/unix/os_str.rs
@@ -14,7 +14,6 @@
 use borrow::Cow;
 use fmt;
 use str;
-use mem;
 use rc::Rc;
 use sync::Arc;
 use sys_common::{AsInner, IntoInner};
@@ -105,7 +104,7 @@ impl Buf {
     }
 
     pub fn as_slice(&self) -> &Slice {
-        unsafe { mem::transmute(&*self.inner) }
+        unsafe { &*(&*self.inner as *const [u8] as *const Slice) }
     }
 
     pub fn into_string(self) -> Result<String, Buf> {
@@ -118,12 +117,13 @@ impl Buf {
 
     #[inline]
     pub fn into_box(self) -> Box<Slice> {
-        unsafe { mem::transmute(self.inner.into_boxed_slice()) }
+        let boxed = self.inner.into_boxed_slice();
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     #[inline]
     pub fn from_box(boxed: Box<Slice>) -> Buf {
-        let inner: Box<[u8]> = unsafe { mem::transmute(boxed) };
+        let inner = unsafe { Box::from_raw(Box::into_raw(boxed) as *mut [u8]) };
         Buf { inner: inner.into_vec() }
     }
 
@@ -140,7 +140,7 @@ impl Buf {
 
 impl Slice {
     fn from_u8_slice(s: &[u8]) -> &Slice {
-        unsafe { mem::transmute(s) }
+        unsafe { &*(s as *const [u8] as *const Slice) }
     }
 
     pub fn from_str(s: &str) -> &Slice {
@@ -162,12 +162,12 @@ impl Slice {
     #[inline]
     pub fn into_box(&self) -> Box<Slice> {
         let boxed: Box<[u8]> = self.inner.into();
-        unsafe { mem::transmute(boxed) }
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     pub fn empty_box() -> Box<Slice> {
         let boxed: Box<[u8]> = Default::default();
-        unsafe { mem::transmute(boxed) }
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     #[inline]
diff --git a/src/libstd/sys/wasm/os_str.rs b/src/libstd/sys/wasm/os_str.rs
index 543c22ebe18a3..17833e12fd824 100644
--- a/src/libstd/sys/wasm/os_str.rs
+++ b/src/libstd/sys/wasm/os_str.rs
@@ -14,7 +14,6 @@
 use borrow::Cow;
 use fmt;
 use str;
-use mem;
 use rc::Rc;
 use sync::Arc;
 use sys_common::{AsInner, IntoInner};
@@ -105,7 +104,7 @@ impl Buf {
     }
 
     pub fn as_slice(&self) -> &Slice {
-        unsafe { mem::transmute(&*self.inner) }
+        unsafe { &*(&*self.inner as *const [u8] as *const Slice) }
     }
 
     pub fn into_string(self) -> Result<String, Buf> {
@@ -118,12 +117,13 @@ impl Buf {
 
     #[inline]
     pub fn into_box(self) -> Box<Slice> {
-        unsafe { mem::transmute(self.inner.into_boxed_slice()) }
+        let boxed = self.inner.into_boxed_slice();
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     #[inline]
     pub fn from_box(boxed: Box<Slice>) -> Buf {
-        let inner: Box<[u8]> = unsafe { mem::transmute(boxed) };
+        let inner = unsafe { Box::from_raw(Box::into_raw(boxed) as *mut [u8]) };
         Buf { inner: inner.into_vec() }
     }
 
@@ -140,7 +140,7 @@ impl Buf {
 
 impl Slice {
     fn from_u8_slice(s: &[u8]) -> &Slice {
-        unsafe { mem::transmute(s) }
+        unsafe { &*(s as *const [u8] as *const Slice) }
     }
 
     pub fn from_str(s: &str) -> &Slice {
@@ -162,12 +162,12 @@ impl Slice {
     #[inline]
     pub fn into_box(&self) -> Box<Slice> {
         let boxed: Box<[u8]> = self.inner.into();
-        unsafe { mem::transmute(boxed) }
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     pub fn empty_box() -> Box<Slice> {
         let boxed: Box<[u8]> = Default::default();
-        unsafe { mem::transmute(boxed) }
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     #[inline]
diff --git a/src/libstd/sys/windows/os_str.rs b/src/libstd/sys/windows/os_str.rs
index 414c9c5418e45..baa20ff80490f 100644
--- a/src/libstd/sys/windows/os_str.rs
+++ b/src/libstd/sys/windows/os_str.rs
@@ -14,7 +14,6 @@
 use borrow::Cow;
 use fmt;
 use sys_common::wtf8::{Wtf8, Wtf8Buf};
-use mem;
 use rc::Rc;
 use sync::Arc;
 use sys_common::{AsInner, IntoInner, FromInner};
@@ -90,7 +89,7 @@ impl Buf {
     }
 
     pub fn as_slice(&self) -> &Slice {
-        unsafe { mem::transmute(self.inner.as_slice()) }
+        unsafe { &*(self.inner.as_slice() as *const Wtf8 as *const Slice) }
     }
 
     pub fn into_string(self) -> Result<String, Buf> {
@@ -115,12 +114,13 @@ impl Buf {
 
     #[inline]
     pub fn into_box(self) -> Box<Slice> {
-        unsafe { mem::transmute(self.inner.into_box()) }
+        let boxed = self.inner.into_box();
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     #[inline]
     pub fn from_box(boxed: Box<Slice>) -> Buf {
-        let inner: Box<Wtf8> = unsafe { mem::transmute(boxed) };
+        let inner = unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Wtf8) };
         Buf { inner: Wtf8Buf::from_box(inner) }
     }
 
@@ -137,7 +137,7 @@ impl Buf {
 
 impl Slice {
     pub fn from_str(s: &str) -> &Slice {
-        unsafe { mem::transmute(Wtf8::from_str(s)) }
+        unsafe { &*(Wtf8::from_str(s) as *const Wtf8 as *const Slice) }
     }
 
     pub fn to_str(&self) -> Option<&str> {
@@ -156,11 +156,13 @@ impl Slice {
 
     #[inline]
     pub fn into_box(&self) -> Box<Slice> {
-        unsafe { mem::transmute(self.inner.into_box()) }
+        let boxed = self.inner.into_box();
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     pub fn empty_box() -> Box<Slice> {
-        unsafe { mem::transmute(Wtf8::empty_box()) }
+        let boxed = Wtf8::empty_box();
+        unsafe { Box::from_raw(Box::into_raw(boxed) as *mut Slice) }
     }
 
     #[inline]
diff --git a/src/libstd_unicode/lossy.rs b/src/libstd_unicode/lossy.rs
index cc8e93308a527..592468ff7f40e 100644
--- a/src/libstd_unicode/lossy.rs
+++ b/src/libstd_unicode/lossy.rs
@@ -12,7 +12,6 @@ use core::str as core_str;
 use core::fmt;
 use core::fmt::Write;
 use char;
-use core::mem;
 
 
 /// Lossy UTF-8 string.
@@ -27,7 +26,7 @@ impl Utf8Lossy {
     }
 
     pub fn from_bytes(bytes: &[u8]) -> &Utf8Lossy {
-        unsafe { mem::transmute(bytes) }
+        unsafe { &*(bytes as *const [u8] as *const Utf8Lossy) }
     }
 
     pub fn chunks(&self) -> Utf8LossyChunksIter {