2 files changed, 2 insertions, 1 deletions
diff --git a/compiler/rustc_data_structures/src/lib.rs b/compiler/rustc_data_structures/src/lib.rs
index 88c160e93b6..06718cc9803 100644
--- a/compiler/rustc_data_structures/src/lib.rs
+++ b/compiler/rustc_data_structures/src/lib.rs
@@ -14,6 +14,7 @@
 #![feature(generators)]
 #![feature(generator_trait)]
 #![feature(fn_traits)]
+#![feature(int_bits_const)]
 #![feature(min_specialization)]
 #![feature(optin_builtin_traits)]
 #![feature(nll)]
diff --git a/compiler/rustc_data_structures/src/tagged_ptr/copy.rs b/compiler/rustc_data_structures/src/tagged_ptr/copy.rs
index d39d146db31..d63bcdb3c2b 100644
--- a/compiler/rustc_data_structures/src/tagged_ptr/copy.rs
+++ b/compiler/rustc_data_structures/src/tagged_ptr/copy.rs
@@ -48,7 +48,7 @@ where
     P: Pointer,
     T: Tag,
 {
-    const TAG_BIT_SHIFT: usize = (8 * std::mem::size_of::<usize>()) - T::BITS;
+    const TAG_BIT_SHIFT: usize = usize::BITS as usize - T::BITS;
     const ASSERTION: () = {
         assert!(T::BITS <= P::BITS);
         // Used for the transmute_copy's below