diff --git a/library/core/src/mem/mod.rs b/library/core/src/mem/mod.rs
index e84014c68a676..70c3fded692d9 100644
--- a/library/core/src/mem/mod.rs
+++ b/library/core/src/mem/mod.rs
@@ -374,7 +374,8 @@ pub const fn size_of_val<T: ?Sized>(val: &T) -> usize {
 /// ```
 #[inline]
 #[unstable(feature = "layout_for_ptr", issue = "69835")]
-pub unsafe fn size_of_val_raw<T: ?Sized>(val: *const T) -> usize {
+#[rustc_const_unstable(feature = "const_size_of_val_raw", issue = "46571")]
+pub const unsafe fn size_of_val_raw<T: ?Sized>(val: *const T) -> usize {
     intrinsics::size_of_val(val)
 }
 
@@ -505,7 +506,8 @@ pub const fn align_of_val<T: ?Sized>(val: &T) -> usize {
 /// ```
 #[inline]
 #[unstable(feature = "layout_for_ptr", issue = "69835")]
-pub unsafe fn align_of_val_raw<T: ?Sized>(val: *const T) -> usize {
+#[rustc_const_unstable(feature = "const_align_of_val_raw", issue = "46571")]
+pub const unsafe fn align_of_val_raw<T: ?Sized>(val: *const T) -> usize {
     intrinsics::min_align_of_val(val)
 }
 
diff --git a/src/test/ui/consts/const-size_of_val-align_of_val.rs b/src/test/ui/consts/const-size_of_val-align_of_val.rs
index e8e6f1d390099..5c0d7d94d64f1 100644
--- a/src/test/ui/consts/const-size_of_val-align_of_val.rs
+++ b/src/test/ui/consts/const-size_of_val-align_of_val.rs
@@ -1,6 +1,7 @@
 // run-pass
 
 #![feature(const_size_of_val, const_align_of_val)]
+#![feature(const_size_of_val_raw, const_align_of_val_raw, layout_for_ptr)]
 
 use std::mem;
 
@@ -32,6 +33,9 @@ const ALIGN_OF_UGH: usize = mem::align_of_val(&UGH);
 
 const SIZE_OF_SLICE: usize = mem::size_of_val("foobar".as_bytes());
 
+const SIZE_OF_DANGLING: usize = unsafe { mem::size_of_val_raw(0x100 as *const i32) };
+const ALIGN_OF_DANGLING: usize = unsafe { mem::align_of_val_raw(0x100 as *const i16) };
+
 fn main() {
     assert_eq!(SIZE_OF_FOO, mem::size_of::<Foo>());
     assert_eq!(SIZE_OF_BAR, mem::size_of::<Bar>());
@@ -41,5 +45,8 @@ fn main() {
     assert_eq!(ALIGN_OF_BAR, mem::align_of::<Bar>());
     assert_eq!(ALIGN_OF_UGH, mem::align_of::<Ugh>());
 
+    assert_eq!(SIZE_OF_DANGLING, mem::size_of::<i32>());
+    assert_eq!(ALIGN_OF_DANGLING, mem::align_of::<i16>());
+
     assert_eq!(SIZE_OF_SLICE, "foobar".len());
 }