diff --git a/rust/ares/src/noun.rs b/rust/ares/src/noun.rs
index e7b89aa..c1dbbc4 100644
--- a/rust/ares/src/noun.rs
+++ b/rust/ares/src/noun.rs
@@ -144,7 +144,7 @@ impl DirectAtom {
         Atom { direct: self }
     }
 
-    pub fn as_ubig(self, _stack: &mut dyn Stack) -> UBig {
+    pub fn as_ubig<S: Stack>(self, _stack: &mut S) -> UBig {
         UBig::from(self.0)
     }
 
@@ -362,7 +362,7 @@ impl IndirectAtom {
         BitSlice::from_slice(self.as_slice())
     }
 
-    pub fn as_ubig(&self, stack: &mut dyn Stack) -> UBig {
+    pub fn as_ubig<S: Stack>(&self, stack: &mut S) -> UBig {
         UBig::from_le_bytes_stack(stack, self.as_bytes())
     }
 
@@ -629,7 +629,7 @@ impl Atom {
         }
     }
 
-    pub fn as_ubig(self, stack: &mut dyn Stack) -> UBig {
+    pub fn as_ubig<S: Stack>(self, stack: &mut S) -> UBig {
         if self.is_indirect() {
             unsafe { self.indirect.as_ubig(stack) }
         } else {
diff --git a/rust/ibig-rs/src/add_ops.rs b/rust/ibig-rs/src/add_ops.rs
index 9591ecf..da98bed 100644
--- a/rust/ibig-rs/src/add_ops.rs
+++ b/rust/ibig-rs/src/add_ops.rs
@@ -531,7 +531,7 @@ impl UBig {
     // given at least 2 words of extra capacity.  However, this supports UBigs which have already
     // been expanded through other operations.
     #[inline]
-    pub fn add_stack(stack: &mut dyn Stack, lhs: UBig, rhs: UBig) -> UBig {
+    pub fn add_stack<S: Stack>(stack: &mut S, lhs: UBig, rhs: UBig) -> UBig {
         match (lhs.into_repr(), rhs.into_repr()) {
             (Small(word0), Small(word1)) => UBig::add_word_stack(stack, word0, word1),
             (Small(word0), Large(buffer1)) => UBig::add_large_word_stack(stack, buffer1, word0),
@@ -548,7 +548,7 @@ impl UBig {
 
     /// Add two `Word`s.
     #[inline]
-    fn add_word_stack(stack: &mut dyn Stack, a: Word, b: Word) -> UBig {
+    fn add_word_stack<S: Stack>(stack: &mut S, a: Word, b: Word) -> UBig {
         let (res, overflow) = a.overflowing_add(b);
         if overflow {
             let mut buffer = Buffer::allocate_stack(stack, 2);
@@ -561,7 +561,7 @@ impl UBig {
     }
 
     /// Add a large number to a `Word`.
-    fn add_large_word_stack(stack: &mut dyn Stack, mut buffer: Buffer, rhs: Word) -> UBig {
+    fn add_large_word_stack<S: Stack>(stack: &mut S, mut buffer: Buffer, rhs: Word) -> UBig {
         debug_assert!(buffer.len() >= 2);
         if add::add_word_in_place(&mut buffer, rhs) {
             buffer.push_may_reallocate_stack(stack, 1);
@@ -570,7 +570,7 @@ impl UBig {
     }
 
     /// Add two large numbers.
-    fn add_large_stack(stack: &mut dyn Stack, mut buffer: Buffer, rhs: &[Word]) -> UBig {
+    fn add_large_stack<S: Stack>(stack: &mut S, mut buffer: Buffer, rhs: &[Word]) -> UBig {
         let n = buffer.len().min(rhs.len());
         let overflow = add::add_same_len_in_place(&mut buffer[..n], &rhs[..n]);
         if rhs.len() > n {
@@ -622,7 +622,7 @@ impl UBig {
 
     // Subtraction is always in-place
     #[inline]
-    pub fn sub_stack(_stack: &mut dyn Stack, lhs: UBig, rhs: UBig) -> UBig {
+    pub fn sub_stack<S: Stack>(_stack: &mut S, lhs: UBig, rhs: UBig) -> UBig {
         lhs - rhs
     }
 
diff --git a/rust/ibig-rs/src/buffer.rs b/rust/ibig-rs/src/buffer.rs
index f692d50..cd39913 100644
--- a/rust/ibig-rs/src/buffer.rs
+++ b/rust/ibig-rs/src/buffer.rs
@@ -21,7 +21,7 @@ use core::{
 pub(crate) struct Buffer(ManuallyDrop<Vec<Word>>);
 
 impl Buffer {
-    pub(crate) fn allocate_stack(stack: &mut dyn Stack, num_words: usize) -> Buffer {
+    pub(crate) fn allocate_stack<S: Stack>(stack: &mut S, num_words: usize) -> Buffer {
         if num_words > Buffer::MAX_CAPACITY {
             UBig::panic_number_too_large();
         }
@@ -44,7 +44,7 @@ impl Buffer {
         )))
     }
 
-    pub(crate) fn ensure_capacity_stack(&mut self, stack: &mut dyn Stack, num_words: usize) {
+    pub(crate) fn ensure_capacity_stack<S: Stack>(&mut self, stack: &mut S, num_words: usize) {
         if num_words > self.capacity() {
             self.reallocate_stack(stack, num_words);
         }
@@ -69,7 +69,7 @@ impl Buffer {
         // }
     }
 
-    fn reallocate_stack(&mut self, stack: &mut dyn Stack, num_words: usize) {
+    fn reallocate_stack<S: Stack>(&mut self, stack: &mut S, num_words: usize) {
         assert!(num_words >= self.len());
         let mut new_buffer = Buffer::allocate_stack(stack, num_words);
         new_buffer.clone_from(self);
@@ -106,7 +106,7 @@ impl Buffer {
     }
 
     #[inline]
-    pub(crate) fn push_may_reallocate_stack(&mut self, stack: &mut dyn Stack, word: Word) {
+    pub(crate) fn push_may_reallocate_stack<S: Stack>(&mut self, stack: &mut S, word: Word) {
         self.ensure_capacity_stack(stack, self.len() + 1);
         self.push(word);
     }
diff --git a/rust/ibig-rs/src/convert.rs b/rust/ibig-rs/src/convert.rs
index 59d5e66..3109191 100644
--- a/rust/ibig-rs/src/convert.rs
+++ b/rust/ibig-rs/src/convert.rs
@@ -31,7 +31,7 @@ impl Default for IBig {
 
 impl UBig {
     #[inline]
-    pub fn from_le_bytes_stack(stack: &mut dyn Stack, bytes: &[u8]) -> UBig {
+    pub fn from_le_bytes_stack<S: Stack>(stack: &mut S, bytes: &[u8]) -> UBig {
         if bytes.len() <= WORD_BYTES {
             // fast path
             UBig::from_word(primitive::word_from_le_bytes_partial(bytes))
@@ -40,7 +40,7 @@ impl UBig {
         }
     }
 
-    fn from_le_bytes_large_stack(stack: &mut dyn Stack, bytes: &[u8]) -> UBig {
+    fn from_le_bytes_large_stack<S: Stack>(stack: &mut S, bytes: &[u8]) -> UBig {
         debug_assert!(bytes.len() > WORD_BYTES);
         let mut buffer = Buffer::allocate_stack(stack, (bytes.len() - 1) / WORD_BYTES + 1);
         let mut chunks = bytes.chunks_exact(WORD_BYTES);
@@ -552,7 +552,7 @@ impl TryFrom<&IBig> for UBig {
 
 impl UBig {
     #[inline]
-    pub(crate) fn from_unsigned_stack<T>(stack: &mut dyn Stack, x: T) -> UBig
+    pub(crate) fn from_unsigned_stack<S: Stack, T>(stack: &mut S, x: T) -> UBig
     where
         T: PrimitiveUnsigned,
     {
diff --git a/rust/ibig-rs/src/div_ops.rs b/rust/ibig-rs/src/div_ops.rs
index 6f0b5fb..1448a6a 100644
--- a/rust/ibig-rs/src/div_ops.rs
+++ b/rust/ibig-rs/src/div_ops.rs
@@ -1279,7 +1279,7 @@ impl_div_ibig_signed!(isize);
 
 impl UBig {
     #[inline]
-    pub fn div_stack(stack: &mut dyn Stack, lhs: UBig, rhs: UBig) -> UBig {
+    pub fn div_stack<S: Stack>(stack: &mut S, lhs: UBig, rhs: UBig) -> UBig {
         match (lhs.into_repr(), rhs.into_repr()) {
             (Small(word0), Small(word1)) => UBig::div_word(word0, word1),
             (Small(_), Large(_)) => UBig::from_word(0),
@@ -1295,7 +1295,7 @@ impl UBig {
     }
 
     #[inline]
-    pub fn rem_stack(stack: &mut dyn Stack, lhs: UBig, rhs: UBig) -> UBig {
+    pub fn rem_stack<S: Stack>(stack: &mut S, lhs: UBig, rhs: UBig) -> UBig {
         match (lhs.into_repr(), rhs.into_repr()) {
             (Small(word0), Small(word1)) => UBig::rem_word(word0, word1),
             (Small(word0), Large(_)) => UBig::from_word(word0),
@@ -1311,7 +1311,7 @@ impl UBig {
     }
 
     #[inline]
-    pub fn div_rem_stack(stack: &mut dyn Stack, lhs: UBig, rhs: UBig) -> (UBig, UBig) {
+    pub fn div_rem_stack<S: Stack>(stack: &mut S, lhs: UBig, rhs: UBig) -> (UBig, UBig) {
         match (lhs.into_repr(), rhs.into_repr()) {
             (Small(word0), Small(word1)) => UBig::div_rem_word(word0, word1),
             (Small(word0), Large(_)) => (UBig::from_word(0), UBig::from_word(word0)),
@@ -1327,14 +1327,14 @@ impl UBig {
     }
 
     /// `lhs / rhs`
-    fn div_large_stack(stack: &mut dyn Stack, mut lhs: Buffer, mut rhs: Buffer) -> UBig {
+    fn div_large_stack<S: Stack>(stack: &mut S, mut lhs: Buffer, mut rhs: Buffer) -> UBig {
         let _shift = UBig::div_rem_in_lhs_stack(stack, &mut lhs, &mut rhs);
         lhs.erase_front(rhs.len());
         lhs.into()
     }
 
     /// `lhs % rhs`
-    fn rem_large_stack(stack: &mut dyn Stack, mut lhs: Buffer, mut rhs: Buffer) -> UBig {
+    fn rem_large_stack<S: Stack>(stack: &mut S, mut lhs: Buffer, mut rhs: Buffer) -> UBig {
         let shift = UBig::div_rem_in_lhs_stack(stack, &mut lhs, &mut rhs);
         let n = rhs.len();
         rhs.copy_from_slice(&lhs[..n]);
@@ -1344,8 +1344,8 @@ impl UBig {
     }
 
     /// `(lhs / rhs, lhs % rhs)`
-    fn div_rem_large_stack(
-        stack: &mut dyn Stack,
+    fn div_rem_large_stack<S: Stack>(
+        stack: &mut S,
         mut lhs: Buffer,
         mut rhs: Buffer,
     ) -> (UBig, UBig) {
@@ -1361,7 +1361,7 @@ impl UBig {
     /// lhs = (lhs / rhs, lhs % rhs)
     ///
     /// Returns shift.
-    fn div_rem_in_lhs_stack(stack: &mut dyn Stack, lhs: &mut Buffer, rhs: &mut Buffer) -> u32 {
+    fn div_rem_in_lhs_stack<S: Stack>(stack: &mut S, lhs: &mut Buffer, rhs: &mut Buffer) -> u32 {
         let (shift, fast_div_rhs_top) = div::normalize_large(rhs);
         let lhs_carry = shift::shl_in_place(lhs, shift);
         if lhs_carry != 0 {
diff --git a/rust/ibig-rs/src/memory.rs b/rust/ibig-rs/src/memory.rs
index 06783e3..bb67fa8 100644
--- a/rust/ibig-rs/src/memory.rs
+++ b/rust/ibig-rs/src/memory.rs
@@ -9,7 +9,7 @@ pub(crate) struct MemoryAllocation {
     start: *mut u8,
 }
 
-pub trait Stack {
+pub trait Stack: Sized {
     unsafe fn alloc_layout(&mut self, layout: Layout) -> *mut u64;
 }
 
@@ -24,7 +24,7 @@ pub(crate) struct Memory<'a> {
 }
 
 impl MemoryAllocation {
-    pub(crate) fn new_stack(stack: &mut dyn Stack, layout: Layout) -> MemoryAllocation {
+    pub(crate) fn new_stack<S: Stack>(stack: &mut S, layout: Layout) -> MemoryAllocation {
         let start = if layout.size() == 0 {
             // We should use layout.dangling(), but that is unstable.
             layout.align() as *mut u8
diff --git a/rust/ibig-rs/src/mul_ops.rs b/rust/ibig-rs/src/mul_ops.rs
index fe4195f..9ff961c 100644
--- a/rust/ibig-rs/src/mul_ops.rs
+++ b/rust/ibig-rs/src/mul_ops.rs
@@ -300,7 +300,7 @@ impl_mul_ibig_primitive!(isize);
 
 impl UBig {
     #[inline]
-    pub fn mul_stack(stack: &mut dyn Stack, lhs: UBig, rhs: UBig) -> UBig {
+    pub fn mul_stack<S: Stack>(stack: &mut S, lhs: UBig, rhs: UBig) -> UBig {
         match (lhs.into_repr(), rhs.into_repr()) {
             (Small(word0), Small(word1)) => UBig::mul_word_stack(stack, word0, word1),
             (Small(word0), Large(buffer1)) => UBig::mul_large_word_stack(stack, buffer1, word0),
@@ -310,11 +310,11 @@ impl UBig {
     }
 
     #[inline]
-    fn mul_word_stack(stack: &mut dyn Stack, a: Word, b: Word) -> UBig {
+    fn mul_word_stack<S: Stack>(stack: &mut S, a: Word, b: Word) -> UBig {
         UBig::from_unsigned_stack(stack, extend_word(a) * extend_word(b))
     }
 
-    fn mul_large_word_stack(stack: &mut dyn Stack, mut buffer: Buffer, a: Word) -> UBig {
+    fn mul_large_word_stack<S: Stack>(stack: &mut S, mut buffer: Buffer, a: Word) -> UBig {
         match a {
             0 => UBig::from_word(0),
             1 => buffer.into(),
@@ -328,7 +328,7 @@ impl UBig {
         }
     }
 
-    pub fn mul_large_stack(stack: &mut dyn Stack, lhs: &[Word], rhs: &[Word]) -> UBig {
+    pub fn mul_large_stack<S: Stack>(stack: &mut S, lhs: &[Word], rhs: &[Word]) -> UBig {
         debug_assert!(lhs.len() >= 2 && rhs.len() >= 2);
 
         // This may be 1 too large.