diff --git a/src/libcore/simd.rs b/src/libcore/simd.rs
index 54e7d077bb141..42418ccbc1a6f 100644
--- a/src/libcore/simd.rs
+++ b/src/libcore/simd.rs
@@ -40,6 +40,7 @@
 #[experimental]
 #[simd]
 #[deriving(Show)]
+#[repr(C)]
 pub struct i8x16(pub i8, pub i8, pub i8, pub i8,
                  pub i8, pub i8, pub i8, pub i8,
                  pub i8, pub i8, pub i8, pub i8,
@@ -48,22 +49,26 @@ pub struct i8x16(pub i8, pub i8, pub i8, pub i8,
 #[experimental]
 #[simd]
 #[deriving(Show)]
+#[repr(C)]
 pub struct i16x8(pub i16, pub i16, pub i16, pub i16,
                  pub i16, pub i16, pub i16, pub i16);
 
 #[experimental]
 #[simd]
 #[deriving(Show)]
+#[repr(C)]
 pub struct i32x4(pub i32, pub i32, pub i32, pub i32);
 
 #[experimental]
 #[simd]
 #[deriving(Show)]
+#[repr(C)]
 pub struct i64x2(pub i64, pub i64);
 
 #[experimental]
 #[simd]
 #[deriving(Show)]
+#[repr(C)]
 pub struct u8x16(pub u8, pub u8, pub u8, pub u8,
                  pub u8, pub u8, pub u8, pub u8,
                  pub u8, pub u8, pub u8, pub u8,
@@ -72,25 +77,30 @@ pub struct u8x16(pub u8, pub u8, pub u8, pub u8,
 #[experimental]
 #[simd]
 #[deriving(Show)]
+#[repr(C)]
 pub struct u16x8(pub u16, pub u16, pub u16, pub u16,
                  pub u16, pub u16, pub u16, pub u16);
 
 #[experimental]
 #[simd]
 #[deriving(Show)]
+#[repr(C)]
 pub struct u32x4(pub u32, pub u32, pub u32, pub u32);
 
 #[experimental]
 #[simd]
 #[deriving(Show)]
+#[repr(C)]
 pub struct u64x2(pub u64, pub u64);
 
 #[experimental]
 #[simd]
 #[deriving(Show)]
+#[repr(C)]
 pub struct f32x4(pub f32, pub f32, pub f32, pub f32);
 
 #[experimental]
 #[simd]
 #[deriving(Show)]
+#[repr(C)]
 pub struct f64x2(pub f64, pub f64);
diff --git a/src/libgreen/context.rs b/src/libgreen/context.rs
index b63758cdcc5e7..dfed121b3cee1 100644
--- a/src/libgreen/context.rs
+++ b/src/libgreen/context.rs
@@ -15,6 +15,7 @@ use std::rt::stack;
 use std::raw;
 #[cfg(target_arch = "x86_64")]
 use std::simd;
+use libc;
 
 // FIXME #7761: Registers is boxed so that it is 16-byte aligned, for storing
 // SSE regs.  It would be marginally better not to do this. In C++ we
@@ -69,7 +70,7 @@ impl Context {
         // overflow). Additionally, their coroutine stacks are listed as being
         // zero-length, so that's how we detect what's what here.
         let stack_base: *const uint = stack.start();
-        let bounds = if sp as uint == stack_base as uint {
+        let bounds = if sp as libc::uintptr_t == stack_base as libc::uintptr_t {
             None
         } else {
             Some((stack_base as uint, sp as uint))
@@ -165,16 +166,16 @@ fn new_regs() -> Box<Registers> {
 
 #[cfg(target_arch = "x86")]
 fn initialize_call_frame(regs: &mut Registers, fptr: InitFn, arg: uint,
-                         procedure: raw::Procedure, sp: *mut uint) {
+                         procedure: raw::Procedure, sp: *mut libc::uintptr_t) {
 
     // x86 has interesting stack alignment requirements, so do some alignment
     // plus some offsetting to figure out what the actual stack should be.
     let sp = align_down(sp);
     let sp = mut_offset(sp, -4);
 
-    unsafe { *mut_offset(sp, 2) = procedure.env as uint };
-    unsafe { *mut_offset(sp, 1) = procedure.code as uint };
-    unsafe { *mut_offset(sp, 0) = arg as uint };
+    unsafe { *mut_offset(sp, 2) = procedure.env as libc::uintptr_t };
+    unsafe { *mut_offset(sp, 1) = procedure.code as libc::uintptr_t };
+    unsafe { *mut_offset(sp, 0) = arg as libc::uintptr_t };
     let sp = mut_offset(sp, -1);
     unsafe { *sp = 0 }; // The final return address
 
@@ -188,13 +189,15 @@ fn initialize_call_frame(regs: &mut Registers, fptr: InitFn, arg: uint,
 // windows requires saving more registers (both general and XMM), so the windows
 // register context must be larger.
 #[cfg(windows, target_arch = "x86_64")]
+#[repr(C)]
 struct Registers {
-    gpr:[uint, ..14],
+    gpr:[libc::uintptr_t, ..14],
     _xmm:[simd::u32x4, ..10]
 }
 #[cfg(not(windows), target_arch = "x86_64")]
+#[repr(C)]
 struct Registers {
-    gpr:[uint, ..10],
+    gpr:[libc::uintptr_t, ..10],
     _xmm:[simd::u32x4, ..6]
 }
 
@@ -234,30 +237,30 @@ fn initialize_call_frame(regs: &mut Registers, fptr: InitFn, arg: uint,
     unsafe { *sp = 0; }
 
     rtdebug!("creating call frame");
-    rtdebug!("fptr {:#x}", fptr as uint);
+    rtdebug!("fptr {:#x}", fptr as libc::uintptr_t);
     rtdebug!("arg {:#x}", arg);
     rtdebug!("sp {}", sp);
 
     // These registers are frobbed by rust_bootstrap_green_task into the right
     // location so we can invoke the "real init function", `fptr`.
-    regs.gpr[RUSTRT_R12] = arg as uint;
-    regs.gpr[RUSTRT_R13] = procedure.code as uint;
-    regs.gpr[RUSTRT_R14] = procedure.env as uint;
-    regs.gpr[RUSTRT_R15] = fptr as uint;
+    regs.gpr[RUSTRT_R12] = arg as libc::uintptr_t;
+    regs.gpr[RUSTRT_R13] = procedure.code as libc::uintptr_t;
+    regs.gpr[RUSTRT_R14] = procedure.env as libc::uintptr_t;
+    regs.gpr[RUSTRT_R15] = fptr as libc::uintptr_t;
 
     // These registers are picked up by the regular context switch paths. These
     // will put us in "mostly the right context" except for frobbing all the
     // arguments to the right place. We have the small trampoline code inside of
     // rust_bootstrap_green_task to do that.
-    regs.gpr[RUSTRT_RSP] = sp as uint;
-    regs.gpr[RUSTRT_IP] = rust_bootstrap_green_task as uint;
+    regs.gpr[RUSTRT_RSP] = sp as libc::uintptr_t;
+    regs.gpr[RUSTRT_IP] = rust_bootstrap_green_task as libc::uintptr_t;
 
     // Last base pointer on the stack should be 0
     regs.gpr[RUSTRT_RBP] = 0;
 }
 
 #[cfg(target_arch = "arm")]
-type Registers = [uint, ..32];
+type Registers = [libc::uintptr_t, ..32];
 
 #[cfg(target_arch = "arm")]
 fn new_regs() -> Box<Registers> { box {[0, .. 32]} }
@@ -277,17 +280,17 @@ fn initialize_call_frame(regs: &mut Registers, fptr: InitFn, arg: uint,
     // ARM uses the same technique as x86_64 to have a landing pad for the start
     // of all new green tasks. Neither r1/r2 are saved on a context switch, so
     // the shim will copy r3/r4 into r1/r2 and then execute the function in r5
-    regs[0] = arg as uint;              // r0
-    regs[3] = procedure.code as uint;   // r3
-    regs[4] = procedure.env as uint;    // r4
-    regs[5] = fptr as uint;             // r5
-    regs[13] = sp as uint;                          // #52 sp, r13
-    regs[14] = rust_bootstrap_green_task as uint;   // #56 pc, r14 --> lr
+    regs[0] = arg as libc::uintptr_t;              // r0
+    regs[3] = procedure.code as libc::uintptr_t;   // r3
+    regs[4] = procedure.env as libc::uintptr_t;    // r4
+    regs[5] = fptr as libc::uintptr_t;             // r5
+    regs[13] = sp as libc::uintptr_t;                          // #52 sp, r13
+    regs[14] = rust_bootstrap_green_task as libc::uintptr_t;   // #56 pc, r14 --> lr
 }
 
 #[cfg(target_arch = "mips")]
 #[cfg(target_arch = "mipsel")]
-type Registers = [uint, ..32];
+type Registers = [libc::uintptr_t, ..32];
 
 #[cfg(target_arch = "mips")]
 #[cfg(target_arch = "mipsel")]
@@ -304,16 +307,16 @@ fn initialize_call_frame(regs: &mut Registers, fptr: InitFn, arg: uint,
     // The final return address. 0 indicates the bottom of the stack
     unsafe { *sp = 0; }
 
-    regs[4] = arg as uint;
-    regs[5] = procedure.code as uint;
-    regs[6] = procedure.env as uint;
-    regs[29] = sp as uint;
-    regs[25] = fptr as uint;
-    regs[31] = fptr as uint;
+    regs[4] = arg as libc::uintptr_t;
+    regs[5] = procedure.code as libc::uintptr_t;
+    regs[6] = procedure.env as libc::uintptr_t;
+    regs[29] = sp as libc::uintptr_t;
+    regs[25] = fptr as libc::uintptr_t;
+    regs[31] = fptr as libc::uintptr_t;
 }
 
 fn align_down(sp: *mut uint) -> *mut uint {
-    let sp = (sp as uint) & !(16 - 1);
+    let sp = (sp as libc::uintptr_t) & !(16 - 1);
     sp as *mut uint
 }
 
diff --git a/src/libgreen/stack.rs b/src/libgreen/stack.rs
index 601758f8a25df..eea5105de8c72 100644
--- a/src/libgreen/stack.rs
+++ b/src/libgreen/stack.rs
@@ -68,7 +68,7 @@ impl Stack {
 
         // FIXME: Using the FFI to call a C macro. Slow
         stk.valgrind_id = unsafe {
-            rust_valgrind_stack_register(stk.start(), stk.end())
+            rust_valgrind_stack_register(stk.start() as *const libc::uintptr_t, stk.end() as *const libc::uintptr_t)
         };
         return stk;
     }
diff --git a/src/libnative/io/c_unix.rs b/src/libnative/io/c_unix.rs
index d22ce25c778d7..fa7da1de914b4 100644
--- a/src/libnative/io/c_unix.rs
+++ b/src/libnative/io/c_unix.rs
@@ -107,13 +107,14 @@ mod select {
 #[cfg(target_os = "linux")]
 mod select {
     use std::uint;
+    use libc;
 
     pub static FD_SETSIZE: uint = 1024;
 
     #[repr(C)]
     pub struct fd_set {
         // FIXME: shouldn't this be a c_ulong?
-        fds_bits: [uint, ..(FD_SETSIZE / uint::BITS)]
+        fds_bits: [libc::uintptr_t, ..(FD_SETSIZE / uint::BITS)]
     }
 
     pub fn fd_set(set: &mut fd_set, fd: i32) {