diff --git a/src/lib.rs b/src/lib.rs
index 80a47c8526..b0b6d99436 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -10,7 +10,7 @@
 #![feature(nonzero_ops)]
 #![feature(let_chains)]
 #![feature(lint_reasons)]
-#![feature(int_roundings)]
+#![cfg_attr(not(bootstrap), feature(trait_upcasting))]
 // Configure clippy and other lints
 #![allow(
     clippy::collapsible_else_if,
diff --git a/tests/fail/dyn-upcast-trait-mismatch.rs b/tests/fail/dyn-upcast-trait-mismatch.rs
index 7d46ecd8f6..648ac07c43 100644
--- a/tests/fail/dyn-upcast-trait-mismatch.rs
+++ b/tests/fail/dyn-upcast-trait-mismatch.rs
@@ -1,3 +1,6 @@
+#![feature(trait_upcasting)]
+#![allow(incomplete_features)]
+
 trait Foo: PartialEq<i32> + std::fmt::Debug + Send + Sync {
     fn a(&self) -> i32 {
         10
diff --git a/tests/pass/box-custom-alloc.rs b/tests/pass/box-custom-alloc.rs
index 75b512f6f7..8d6da0733f 100644
--- a/tests/pass/box-custom-alloc.rs
+++ b/tests/pass/box-custom-alloc.rs
@@ -1,6 +1,7 @@
 //@revisions: stack tree
 //@[tree]compile-flags: -Zmiri-tree-borrows
-#![feature(allocator_api)]
+#![allow(incomplete_features)] // for trait upcasting
+#![feature(allocator_api, trait_upcasting)]
 
 use std::alloc::Layout;
 use std::alloc::{AllocError, Allocator};
diff --git a/tests/pass/dyn-upcast.rs b/tests/pass/dyn-upcast.rs
index ddaefeca3a..8432012a9b 100644
--- a/tests/pass/dyn-upcast.rs
+++ b/tests/pass/dyn-upcast.rs
@@ -1,3 +1,6 @@
+#![feature(trait_upcasting)]
+#![allow(incomplete_features)]
+
 fn main() {
     basic();
     diamond();