diff --git a/pdl-compiler/src/backends/rust/parser.rs b/pdl-compiler/src/backends/rust/parser.rs
index 050abbf..379d294 100644
--- a/pdl-compiler/src/backends/rust/parser.rs
+++ b/pdl-compiler/src/backends/rust/parser.rs
@@ -429,7 +429,7 @@ impl<'a> FieldParser<'a> {
                 // The element width is not known, but the array
                 // element count is known statically. Parse elements
                 // item by item as an array.
-                let count = syn::Index::from(*count);
+                let count = proc_macro2::Literal::usize_unsuffixed(*count);
                 self.tokens.extend(quote! {
                     // TODO(mgeisler): use
                     // https://doc.rust-lang.org/std/array/fn.try_from_fn.html
@@ -466,12 +466,12 @@ impl<'a> FieldParser<'a> {
             (ElementWidth::Static(element_width), ArrayShape::Static(count)) => {
                 // The element width is known, and the array element
                 // count is known statically.
-                let count = syn::Index::from(*count);
+                let count = proc_macro2::Literal::usize_unsuffixed(*count);
                 // This creates a nicely formatted size.
                 let array_size = if element_width == 1 {
                     quote!(#count)
                 } else {
-                    let element_width = syn::Index::from(element_width);
+                    let element_width = proc_macro2::Literal::usize_unsuffixed(element_width);
                     quote!(#count * #element_width)
                 };
                 self.check_size(&span, &quote! { #array_size });
@@ -511,7 +511,7 @@ impl<'a> FieldParser<'a> {
                 };
                 let count_field = format_ident!("{id}_count");
                 let array_count = if element_width != 1 {
-                    let element_width = syn::Index::from(element_width);
+                    let element_width = proc_macro2::Literal::usize_unsuffixed(element_width);
                     self.tokens.extend(quote! {
                         if #array_size % #element_width != 0 {
                             return Err(DecodeError::InvalidArraySize {
@@ -738,7 +738,7 @@ impl<'a> FieldParser<'a> {
                 0,
                 "Payload field offset from end of packet is not a multiple of 8"
             );
-            let offset_from_end = syn::Index::from(offset_from_end / 8);
+            let offset_from_end = proc_macro2::Literal::usize_unsuffixed(offset_from_end / 8);
             self.check_size(self.span, &quote!(#offset_from_end));
             self.tokens.extend(quote! {
                 let payload = #span[..#span.len() - #offset_from_end].to_vec();
diff --git a/pdl-compiler/src/backends/rust/serializer.rs b/pdl-compiler/src/backends/rust/serializer.rs
index 0af464c..22d5abe 100644
--- a/pdl-compiler/src/backends/rust/serializer.rs
+++ b/pdl-compiler/src/backends/rust/serializer.rs
@@ -59,7 +59,7 @@ impl std::ops::AddAssign<&RuntimeSize> for RuntimeSize {
 
 impl quote::ToTokens for RuntimeSize {
     fn to_tokens(&self, tokens: &mut proc_macro2::TokenStream) {
-        let constant = syn::Index::from(self.constant);
+        let constant = proc_macro2::Literal::usize_unsuffixed(self.constant);
         tokens.extend(match self {
             RuntimeSize { variable, .. } if variable.is_empty() => quote! { #constant },
             RuntimeSize { variable, constant: 0 } => quote! { #(#variable)+* },
@@ -336,11 +336,12 @@ impl Encoder {
                     }
                     (ast::FieldDesc::Array { width: Some(width), .. }, _)
                     | (ast::FieldDesc::Array { .. }, Some(ast::DeclDesc::Enum { width, .. })) => {
-                        let byte_width = syn::Index::from(width / 8);
-                        if byte_width.index == 1 {
+                        let size = width / 8;
+                        if size == 1 {
                             quote! { self.#field_name.len() }
                         } else {
-                            quote! { (self.#field_name.len() * #byte_width) }
+                            let size = proc_macro2::Literal::usize_unsuffixed(size);
+                            quote! { (self.#field_name.len() * #size) }
                         }
                     }
                     (ast::FieldDesc::Array { .. }, _) => {
@@ -467,7 +468,7 @@ impl Encoder {
         self.tokens.extend(match values.as_slice() {
             [] => {
                 let buf = format_ident!("{}", self.buf);
-                let count = syn::Index::from(self.bit_shift / 8);
+                let count = proc_macro2::Literal::usize_unsuffixed(self.bit_shift / 8);
                 quote! {
                     #buf.put_bytes(0, #count);
                 }