diff --git a/library/core/src/intrinsics/simd.rs b/library/core/src/intrinsics/simd.rs
index 30734c020b39b..0c21e6f31a827 100644
--- a/library/core/src/intrinsics/simd.rs
+++ b/library/core/src/intrinsics/simd.rs
@@ -243,18 +243,6 @@ extern "rust-intrinsic" {
     #[rustc_nounwind]
     pub fn simd_shuffle<T, U, V>(x: T, y: T, idx: U) -> V;
 
-    /// Shuffle two vectors by const indices.
-    ///
-    /// `T` must be a vector.
-    ///
-    /// `U` must be a vector with the same element type as `T` and the same length as `IDX`.
-    ///
-    /// Returns a new vector such that element `i` is selected from `xy[IDX[i]]`, where `xy`
-    /// is the concatenation of `x` and `y`. It is a compile-time error if `IDX[i]` is out-of-bounds
-    /// of `xy`.
-    #[rustc_nounwind]
-    pub fn simd_shuffle_generic<T, U, const IDX: &'static [u32]>(x: T, y: T) -> U;
-
     /// Read a vector of pointers.
     ///
     /// `T` must be a vector.
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 0ec46412e9522..02cb02dce1d87 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -249,7 +249,6 @@
 #![feature(transparent_unions)]
 #![feature(try_blocks)]
 #![feature(unboxed_closures)]
-#![feature(unsized_const_params)]
 #![feature(unsized_fn_params)]
 #![feature(with_negative_coherence)]
 // tidy-alphabetical-end
diff --git a/library/core/src/marker.rs b/library/core/src/marker.rs
index a87528033c03b..cf428e36ea7a0 100644
--- a/library/core/src/marker.rs
+++ b/library/core/src/marker.rs
@@ -42,6 +42,8 @@ use crate::hash::Hasher;
 /// }
 /// ```
 #[unstable(feature = "internal_impls_macro", issue = "none")]
+// Allow implementations of `UnsizedConstParamTy` even though std cannot use that feature.
+#[allow_internal_unstable(unsized_const_params)]
 macro marker_impls {
     ( $(#[$($meta:tt)*])* $Trait:ident for $({$($bounds:tt)*})? $T:ty $(, $($rest:tt)*)? ) => {
         $(#[$($meta)*])* impl< $($($bounds)*)? > $Trait for $T {}
diff --git a/src/tools/miri/tests/pass/intrinsics/portable-simd.rs b/src/tools/miri/tests/pass/intrinsics/portable-simd.rs
index 03d9fc0a76fe1..c4ba11d0a436f 100644
--- a/src/tools/miri/tests/pass/intrinsics/portable-simd.rs
+++ b/src/tools/miri/tests/pass/intrinsics/portable-simd.rs
@@ -1,10 +1,23 @@
 //@compile-flags: -Zmiri-strict-provenance
-#![feature(portable_simd, adt_const_params, core_intrinsics, repr_simd)]
+#![feature(
+    portable_simd,
+    unsized_const_params,
+    adt_const_params,
+    rustc_attrs,
+    intrinsics,
+    core_intrinsics,
+    repr_simd
+)]
 #![allow(incomplete_features, internal_features)]
 use std::intrinsics::simd as intrinsics;
 use std::ptr;
 use std::simd::{prelude::*, StdFloat};
 
+extern "rust-intrinsic" {
+    #[rustc_nounwind]
+    pub fn simd_shuffle_generic<T, U, const IDX: &'static [u32]>(x: T, y: T) -> U;
+}
+
 fn simd_ops_f32() {
     let a = f32x4::splat(10.0);
     let b = f32x4::from_array([1.0, 2.0, 3.0, -4.0]);