diff --git a/cargo-miri/src/phases.rs b/cargo-miri/src/phases.rs
index ca8b35a17b..b774ca8fa7 100644
--- a/cargo-miri/src/phases.rs
+++ b/cargo-miri/src/phases.rs
@@ -412,8 +412,11 @@ pub fn phase_rustc(mut args: impl Iterator<Item = String>, phase: RustcPhase) {
     // Arguments are treated very differently depending on whether this crate is
     // for interpretation by Miri, or for use by a build script / proc macro.
     if target_crate {
-        // Set the sysroot.
-        cmd.arg("--sysroot").arg(env::var_os("MIRI_SYSROOT").unwrap());
+        if phase != RustcPhase::Setup {
+            // Set the sysroot -- except during setup, where we don't have an existing sysroot yet
+            // and where the bootstrap wrapper adds its own `--sysroot` flag so we can't set ours.
+            cmd.arg("--sysroot").arg(env::var_os("MIRI_SYSROOT").unwrap());
+        }
 
         // Forward arguments, but patched.
         let emit_flag = "--emit";
@@ -578,9 +581,9 @@ pub fn phase_runner(mut binary_args: impl Iterator<Item = String>, phase: Runner
     }
 
     if phase != RunnerPhase::Rustdoc {
-        // Set the sysroot. Not necessary in rustdoc, where we already set the sysroot when invoking
-        // rustdoc itself, which will forward that flag when invoking rustc (i.e., us), so the flag
-        // is present in `info.args`.
+        // Set the sysroot. Not necessary in rustdoc, where we already set the sysroot in
+        // `phase_rustdoc`. rustdoc will forward that flag when invoking rustc (i.e., us), so the
+        // flag is present in `info.args`.
         cmd.arg("--sysroot").arg(env::var_os("MIRI_SYSROOT").unwrap());
     }
     // Forward rustc arguments.
diff --git a/rust-version b/rust-version
index dfa7f8ca50..bd87405da3 100644
--- a/rust-version
+++ b/rust-version
@@ -1 +1 @@
-63f70b3d104e20289a1a0df82747066c3d85b9a1
+803e33a4460c82581bd01d4008d0f44aef1ddfe8
diff --git a/src/borrow_tracker/mod.rs b/src/borrow_tracker/mod.rs
index 8d76a48826..f21315790a 100644
--- a/src/borrow_tracker/mod.rs
+++ b/src/borrow_tracker/mod.rs
@@ -260,7 +260,7 @@ impl GlobalStateInner {
         &mut self,
         id: AllocId,
         alloc_size: Size,
-        kind: MemoryKind<machine::MiriMemoryKind>,
+        kind: MemoryKind,
         machine: &MiriMachine<'_, '_>,
     ) -> AllocState {
         match self.borrow_tracker_method {
diff --git a/src/borrow_tracker/stacked_borrows/mod.rs b/src/borrow_tracker/stacked_borrows/mod.rs
index 96ff298402..b4005515d9 100644
--- a/src/borrow_tracker/stacked_borrows/mod.rs
+++ b/src/borrow_tracker/stacked_borrows/mod.rs
@@ -509,7 +509,7 @@ impl Stacks {
         id: AllocId,
         size: Size,
         state: &mut GlobalStateInner,
-        kind: MemoryKind<MiriMemoryKind>,
+        kind: MemoryKind,
         machine: &MiriMachine<'_, '_>,
     ) -> Self {
         let (base_tag, perm) = match kind {
diff --git a/src/borrow_tracker/tree_borrows/mod.rs b/src/borrow_tracker/tree_borrows/mod.rs
index a3d49756e4..492e324de4 100644
--- a/src/borrow_tracker/tree_borrows/mod.rs
+++ b/src/borrow_tracker/tree_borrows/mod.rs
@@ -34,7 +34,7 @@ impl<'tcx> Tree {
         id: AllocId,
         size: Size,
         state: &mut GlobalStateInner,
-        _kind: MemoryKind<machine::MiriMemoryKind>,
+        _kind: MemoryKind,
         machine: &MiriMachine<'_, 'tcx>,
     ) -> Self {
         let tag = state.base_ptr_tag(id, machine); // Fresh tag for the root
diff --git a/src/concurrency/data_race.rs b/src/concurrency/data_race.rs
index d51160b283..95049b91cb 100644
--- a/src/concurrency/data_race.rs
+++ b/src/concurrency/data_race.rs
@@ -844,7 +844,7 @@ impl VClockAlloc {
         global: &GlobalState,
         thread_mgr: &ThreadManager<'_, '_>,
         len: Size,
-        kind: MemoryKind<MiriMemoryKind>,
+        kind: MemoryKind,
         current_span: Span,
     ) -> VClockAlloc {
         let (alloc_timestamp, alloc_index) = match kind {
diff --git a/src/diagnostics.rs b/src/diagnostics.rs
index dfbcaaac5c..d44d04e9bf 100644
--- a/src/diagnostics.rs
+++ b/src/diagnostics.rs
@@ -115,7 +115,7 @@ pub enum NonHaltingDiagnostic {
     /// This `Item` was popped from the borrow stack. The string explains the reason.
     PoppedPointerTag(Item, String),
     CreatedCallId(CallId),
-    CreatedAlloc(AllocId, Size, Align, MemoryKind<MiriMemoryKind>),
+    CreatedAlloc(AllocId, Size, Align, MemoryKind),
     FreedAlloc(AllocId),
     AccessedAlloc(AllocId, AccessKind),
     RejectedIsolatedOp(String),
@@ -447,7 +447,7 @@ pub fn report_error<'tcx, 'mir>(
 
 pub fn report_leaks<'mir, 'tcx>(
     ecx: &InterpCx<'mir, 'tcx, MiriMachine<'mir, 'tcx>>,
-    leaks: Vec<(AllocId, MemoryKind<MiriMemoryKind>, Allocation<Provenance, AllocExtra<'tcx>>)>,
+    leaks: Vec<(AllocId, MemoryKind, Allocation<Provenance, AllocExtra<'tcx>>)>,
 ) {
     let mut any_pruned = false;
     for (id, kind, mut alloc) in leaks {
diff --git a/src/lib.rs b/src/lib.rs
index fbe4c9c676..2e19c9ff71 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -128,7 +128,7 @@ pub use crate::eval::{
 };
 pub use crate::helpers::{AccessKind, EvalContextExt as _};
 pub use crate::machine::{
-    AllocExtra, FrameExtra, MiriInterpCx, MiriInterpCxExt, MiriMachine, MiriMemoryKind,
+    AllocExtra, FrameExtra, MemoryKind, MiriInterpCx, MiriInterpCxExt, MiriMachine, MiriMemoryKind,
     PrimitiveLayouts, Provenance, ProvenanceExtra,
 };
 pub use crate::mono_hash_map::MonoHashMap;
diff --git a/src/machine.rs b/src/machine.rs
index ff081328a7..1d06d5c69d 100644
--- a/src/machine.rs
+++ b/src/machine.rs
@@ -135,9 +135,9 @@ pub enum MiriMemoryKind {
     Mmap,
 }
 
-impl From<MiriMemoryKind> for MemoryKind<MiriMemoryKind> {
+impl From<MiriMemoryKind> for MemoryKind {
     #[inline(always)]
-    fn from(kind: MiriMemoryKind) -> MemoryKind<MiriMemoryKind> {
+    fn from(kind: MiriMemoryKind) -> MemoryKind {
         MemoryKind::Machine(kind)
     }
 }
@@ -185,6 +185,8 @@ impl fmt::Display for MiriMemoryKind {
     }
 }
 
+pub type MemoryKind = interpret::MemoryKind<MiriMemoryKind>;
+
 /// Pointer provenance.
 #[derive(Clone, Copy)]
 pub enum Provenance {
@@ -863,10 +865,8 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
     type ProvenanceExtra = ProvenanceExtra;
     type Bytes = Box<[u8]>;
 
-    type MemoryMap = MonoHashMap<
-        AllocId,
-        (MemoryKind<MiriMemoryKind>, Allocation<Provenance, Self::AllocExtra, Self::Bytes>),
-    >;
+    type MemoryMap =
+        MonoHashMap<AllocId, (MemoryKind, Allocation<Provenance, Self::AllocExtra, Self::Bytes>)>;
 
     const GLOBAL_KIND: Option<MiriMemoryKind> = Some(MiriMemoryKind::Global);
 
@@ -1088,7 +1088,7 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
         ecx: &MiriInterpCx<'mir, 'tcx>,
         id: AllocId,
         alloc: Cow<'b, Allocation>,
-        kind: Option<MemoryKind<Self::MemoryKind>>,
+        kind: Option<MemoryKind>,
     ) -> InterpResult<'tcx, Cow<'b, Allocation<Self::Provenance, Self::AllocExtra>>> {
         let kind = kind.expect("we set our STATIC_KIND so this cannot be None");
         if ecx.machine.tracked_alloc_ids.contains(&id) {
@@ -1280,6 +1280,7 @@ impl<'mir, 'tcx> Machine<'mir, 'tcx> for MiriMachine<'mir, 'tcx> {
         (alloc_id, prove_extra): (AllocId, Self::ProvenanceExtra),
         size: Size,
         align: Align,
+        _kind: MemoryKind,
     ) -> InterpResult<'tcx> {
         if machine.tracked_alloc_ids.contains(&alloc_id) {
             machine.emit_diagnostic(NonHaltingDiagnostic::FreedAlloc(alloc_id));
diff --git a/src/shims/os_str.rs b/src/shims/os_str.rs
index 0157c4845c..0409e31d65 100644
--- a/src/shims/os_str.rs
+++ b/src/shims/os_str.rs
@@ -137,7 +137,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     fn alloc_os_str_as_c_str(
         &mut self,
         os_str: &OsStr,
-        memkind: MemoryKind<MiriMemoryKind>,
+        memkind: MemoryKind,
     ) -> InterpResult<'tcx, Pointer<Option<Provenance>>> {
         let size = u64::try_from(os_str.len()).unwrap().checked_add(1).unwrap(); // Make space for `0` terminator.
         let this = self.eval_context_mut();
@@ -153,7 +153,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     fn alloc_os_str_as_wide_str(
         &mut self,
         os_str: &OsStr,
-        memkind: MemoryKind<MiriMemoryKind>,
+        memkind: MemoryKind,
     ) -> InterpResult<'tcx, Pointer<Option<Provenance>>> {
         let size = u64::try_from(os_str.len()).unwrap().checked_add(1).unwrap(); // Make space for `0x0000` terminator.
         let this = self.eval_context_mut();
@@ -230,7 +230,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     fn alloc_path_as_c_str(
         &mut self,
         path: &Path,
-        memkind: MemoryKind<MiriMemoryKind>,
+        memkind: MemoryKind,
     ) -> InterpResult<'tcx, Pointer<Option<Provenance>>> {
         let this = self.eval_context_mut();
         let os_str =
@@ -243,7 +243,7 @@ pub trait EvalContextExt<'mir, 'tcx: 'mir>: crate::MiriInterpCxExt<'mir, 'tcx> {
     fn alloc_path_as_wide_str(
         &mut self,
         path: &Path,
-        memkind: MemoryKind<MiriMemoryKind>,
+        memkind: MemoryKind,
     ) -> InterpResult<'tcx, Pointer<Option<Provenance>>> {
         let this = self.eval_context_mut();
         let os_str =
diff --git a/tests/fail/both_borrows/newtype_pair_retagging.stack.stderr b/tests/fail/both_borrows/newtype_pair_retagging.stack.stderr
index 867907e98e..c26c7f397b 100644
--- a/tests/fail/both_borrows/newtype_pair_retagging.stack.stderr
+++ b/tests/fail/both_borrows/newtype_pair_retagging.stack.stderr
@@ -6,7 +6,7 @@ LL |         Box(unsafe { Unique::new_unchecked(raw) }, alloc)
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
    = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
-help: <TAG> was created by a Unique retag at offsets [0x0..0x4]
+help: <TAG> was created by a SharedReadWrite retag at offsets [0x0..0x4]
   --> $DIR/newtype_pair_retagging.rs:LL:CC
    |
 LL |     let ptr = Box::into_raw(Box::new(0i32));
diff --git a/tests/fail/both_borrows/newtype_retagging.stack.stderr b/tests/fail/both_borrows/newtype_retagging.stack.stderr
index 56715938e9..ae54da70fe 100644
--- a/tests/fail/both_borrows/newtype_retagging.stack.stderr
+++ b/tests/fail/both_borrows/newtype_retagging.stack.stderr
@@ -6,7 +6,7 @@ LL |         Box(unsafe { Unique::new_unchecked(raw) }, alloc)
    |
    = help: this indicates a potential bug in the program: it performed an invalid operation, but the Stacked Borrows rules it violated are still experimental
    = help: see https://github.com/rust-lang/unsafe-code-guidelines/blob/master/wip/stacked-borrows.md for further information
-help: <TAG> was created by a Unique retag at offsets [0x0..0x4]
+help: <TAG> was created by a SharedReadWrite retag at offsets [0x0..0x4]
   --> $DIR/newtype_retagging.rs:LL:CC
    |
 LL |     let ptr = Box::into_raw(Box::new(0i32));
diff --git a/tests/pass/issues/issue-miri-3473.rs b/tests/pass/issues/issue-miri-3473.rs
new file mode 100644
index 0000000000..77b960c1cd
--- /dev/null
+++ b/tests/pass/issues/issue-miri-3473.rs
@@ -0,0 +1,28 @@
+//@revisions: stack tree
+//@[tree]compile-flags: -Zmiri-tree-borrows
+use std::cell::UnsafeCell;
+
+#[repr(C)]
+#[derive(Default)]
+struct Node {
+    _meta: UnsafeCell<usize>,
+    value: usize,
+}
+
+impl Node {
+    fn value(&self) -> &usize {
+        &self.value
+    }
+}
+
+/// This used to cause Stacked Borrows errors because of trouble around conversion
+/// from Box to raw pointer.
+fn main() {
+    unsafe {
+        let a = Box::into_raw(Box::new(Node::default()));
+        let ptr = &*a;
+        *UnsafeCell::raw_get(a.cast::<UnsafeCell<usize>>()) = 2;
+        assert_eq!(*ptr.value(), 0);
+        drop(Box::from_raw(a));
+    }
+}
diff --git a/tests/pass/stacked-borrows/stacked-borrows.rs b/tests/pass/stacked-borrows/stacked-borrows.rs
index 734411ccc7..c75824d7f9 100644
--- a/tests/pass/stacked-borrows/stacked-borrows.rs
+++ b/tests/pass/stacked-borrows/stacked-borrows.rs
@@ -20,6 +20,7 @@ fn main() {
     wide_raw_ptr_in_tuple();
     not_unpin_not_protected();
     write_does_not_invalidate_all_aliases();
+    box_into_raw_allows_interior_mutable_alias();
 }
 
 // Make sure that reading from an `&mut` does, like reborrowing to `&`,
@@ -263,3 +264,16 @@ fn write_does_not_invalidate_all_aliases() {
     other::lib2();
     assert_eq!(*x, 1337); // oops, the value changed! I guess not all pointers were invalidated
 }
+
+fn box_into_raw_allows_interior_mutable_alias() {
+    unsafe {
+        let b = Box::new(std::cell::Cell::new(42));
+        let raw = Box::into_raw(b);
+        let c = &*raw;
+        let d = raw.cast::<i32>(); // bypassing `Cell` -- only okay in Miri tests
+        // `c` and `d` should permit arbitrary aliasing with each other now.
+        *d = 1;
+        c.set(2);
+        drop(Box::from_raw(raw));
+    }
+}