diff --git a/library/stdarch/coresimd/src/v64.rs b/library/stdarch/coresimd/src/v64.rs
index c1e346d1b23a..5b6d0f7e3e0b 100644
--- a/library/stdarch/coresimd/src/v64.rs
+++ b/library/stdarch/coresimd/src/v64.rs
@@ -29,12 +29,20 @@ define_impl! { u8x8, u8, 8, i8x8, x0, x1, x2, x3, x4, x5, x6, x7 }
 define_ty! { i8x8, i8, i8, i8, i8, i8, i8, i8, i8 }
 define_impl! { i8x8, i8, 8, i8x8, x0, x1, x2, x3, x4, x5, x6, x7 }
 
-define_from!(u32x2, i32x2, u16x4, i16x4, u8x8, i8x8);
-define_from!(i32x2, u32x2, u16x4, i16x4, u8x8, i8x8);
-define_from!(u16x4, u32x2, i32x2, i16x4, u8x8, i8x8);
-define_from!(i16x4, u32x2, i32x2, u16x4, u8x8, i8x8);
-define_from!(u8x8, u32x2, i32x2, u16x4, i16x4, i8x8);
-define_from!(i8x8, u32x2, i32x2, u16x4, i16x4, u8x8);
+// On `x86` corresponds to llvm's `x86_mmx` type.
+define_ty_doc! {
+    __m64, i64 |
+    /// 64-bit wide integer vector type.
+}
+define_impl! { __m64, i64, 1, __m64, x0 }
+
+define_from!(u32x2, i32x2, u16x4, i16x4, u8x8, i8x8, __m64);
+define_from!(i32x2, u32x2, u16x4, i16x4, u8x8, i8x8, __m64);
+define_from!(u16x4, u32x2, i32x2, i16x4, u8x8, i8x8, __m64);
+define_from!(i16x4, u32x2, i32x2, u16x4, u8x8, i8x8, __m64);
+define_from!(u8x8, u32x2, i32x2, u16x4, i16x4, i8x8, __m64);
+define_from!(i8x8, u32x2, i32x2, u16x4, i16x4, u8x8, __m64);
+define_from!(__m64, i8x8, u32x2, i32x2, u16x4, i16x4, u8x8);
 
 define_common_ops!(f32x2, u32x2, i32x2, u16x4, i16x4, u8x8, i8x8);
 define_float_ops!(f32x2);
@@ -67,7 +75,9 @@ define_casts!(
     (u16x4, u32x4, as_u32x4),
     (u16x4, i32x4, as_i32x4),
     (u32x2, u64x2, as_u64x2),
-    (u32x2, i64x2, as_i64x2)
+    (u32x2, i64x2, as_i64x2) /* FIXME:
+                              * (__m64, __m128i, as___m128i),
+                              * (__m64, __m256i, as___m256i) */
 );
 
 #[cfg(test)]
diff --git a/library/stdarch/coresimd/src/x86/i686/mmx.rs b/library/stdarch/coresimd/src/x86/i686/mmx.rs
index 54aa8c1bbc53..d4aa35b20a18 100644
--- a/library/stdarch/coresimd/src/x86/i686/mmx.rs
+++ b/library/stdarch/coresimd/src/x86/i686/mmx.rs
@@ -8,8 +8,7 @@
 //!
 //! [intel64_ref]: http://www.intel.de/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-software-developer-instruction-set-reference-manual-325383.pdf
 
-use v64::{i16x4, i32x2, i8x8};
-use x86::__m64;
+use v64::{__m64, i16x4, i32x2, i8x8};
 use core::mem;
 
 #[cfg(test)]
@@ -59,9 +58,8 @@ extern "C" {
 
 #[cfg(test)]
 mod tests {
-    use v64::{i16x4, i32x2, i8x8};
+    use v64::{__m64, i16x4, i32x2, i8x8};
     use x86::i686::mmx;
-    use x86::__m64;
     use stdsimd_test::simd_test;
 
     #[simd_test = "sse"] // FIXME: should be mmx
diff --git a/library/stdarch/coresimd/src/x86/i686/sse.rs b/library/stdarch/coresimd/src/x86/i686/sse.rs
index b632d761735b..a5bd78b285ae 100644
--- a/library/stdarch/coresimd/src/x86/i686/sse.rs
+++ b/library/stdarch/coresimd/src/x86/i686/sse.rs
@@ -1,8 +1,7 @@
 //! `i686` Streaming SIMD Extensions (SSE)
 
 use v128::f32x4;
-use v64::{i16x4, i32x2, i8x8, u16x4, u8x8};
-use x86::__m64;
+use v64::{__m64, i16x4, i32x2, i8x8, u16x4, u8x8};
 use core::mem;
 use x86::i586;
 use x86::i686::mmx;
diff --git a/library/stdarch/coresimd/src/x86/mod.rs b/library/stdarch/coresimd/src/x86/mod.rs
index 79f4a23a2a5b..fcbcdead03dc 100644
--- a/library/stdarch/coresimd/src/x86/mod.rs
+++ b/library/stdarch/coresimd/src/x86/mod.rs
@@ -26,11 +26,6 @@ mod x86_64;
 #[cfg(target_arch = "x86_64")]
 pub use self::x86_64::*;
 
-/// 64-bit wide integer vector type.
-#[allow(non_camel_case_types)]
-#[repr(simd)]
-#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord)]
-pub struct __m64(i64); // corresponds to llvm's `x86_mmx` type
 /// 128-bit wide signed integer vector type
 #[allow(non_camel_case_types)]
 pub type __m128i = ::v128::i8x16;