diff --git a/Cargo.lock b/Cargo.lock
index 6bfa8af1e..960028af5 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -217,7 +217,7 @@ checksum = "523363cbe1df49b68215efdf500b103ac3b0fb4836aed6d15689a076eadb8fff"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.82",
+ "syn 2.0.90",
 ]
 
 [[package]]
@@ -1129,7 +1129,7 @@ checksum = "1bb5c1d8184f13f7d0ccbeeca0def2f9a181bce2624302793005f5ca8aa62e5e"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.82",
+ "syn 2.0.90",
 ]
 
 [[package]]
@@ -1505,7 +1505,7 @@ checksum = "ca414edb151b4c8d125c12566ab0d74dc9cdba36fb80eb7b848c15f495fd32d1"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.82",
+ "syn 2.0.90",
 ]
 
 [[package]]
@@ -1728,7 +1728,7 @@ checksum = "beb382a4d9f53bd5c0be86b10d8179c3f8a14c30bf774ff77096ed6581e35981"
 dependencies = [
  "proc-macro2",
  "quote",
- "syn 2.0.82",
+ "syn 2.0.90",
 ]
 
 [[package]]
diff --git a/ceno_host/src/lib.rs b/ceno_host/src/lib.rs
index c64bce07d..ac90f7d1d 100644
--- a/ceno_host/src/lib.rs
+++ b/ceno_host/src/lib.rs
@@ -8,6 +8,14 @@ use rkyv::{
     util::AlignedVec,
 };
 
+// We want to get access to the default value of `AlignedVec::ALIGNMENT`, and using it directly like this
+//   pub const RKVY_ALIGNMENT: usize = rkyv::util::AlignedVec::ALIGNMENT;
+// doesn't work:
+pub const RKYV_ALIGNMENT: usize = {
+    type AlignedVec = rkyv::util::AlignedVec;
+    AlignedVec::ALIGNMENT
+};
+
 #[derive(Default)]
 pub struct CenoStdin {
     pub items: Vec<AlignedVec>,
@@ -26,32 +34,30 @@ impl CenoStdin {
     }
 
     pub fn finalise(&self) -> Vec<u32> {
-        // TODO: perhaps don't hardcode 16 here.
-        // It's from rkyv's format, so we can probably take it from there somehow?
-        // TODO: clean this up.
-        let initial_offset = (size_of::<u32>() * self.items.len()).next_multiple_of(16);
-        // println!("offset: {}", initial_offset);
+        let initial_offset = (size_of::<u32>() * self.items.len()).next_multiple_of(RKYV_ALIGNMENT);
         let offsets: Vec<u32> = self
             .items
             .iter()
             .scan(initial_offset, |acc, bytes| {
                 let output = (*acc + bytes.len()) as u32;
-                // print!("len: {}\t", bytes.len());
-                *acc += bytes.len().next_multiple_of(16);
-                // println!("acc: {}", *acc);
+                *acc += bytes.len().next_multiple_of(RKYV_ALIGNMENT);
                 Some(output)
             })
             .collect();
         let offsets_u8: Vec<u8> = offsets.iter().copied().flat_map(u32::to_le_bytes).collect();
         let mut buf: AlignedVec = AlignedVec::new();
         buf.extend_from_slice(&offsets_u8);
-        // println!("buf.len() after offsets: {}", buf.len());
-        buf.extend_from_slice(&vec![0; buf.len().next_multiple_of(16) - buf.len()]);
-        // println!("buf.len() after offset padding: {}", buf.len());
+        buf.extend_from_slice(&vec![
+            0;
+            buf.len().next_multiple_of(RKYV_ALIGNMENT) - buf.len()
+        ]);
         for (offset, item) in izip!(offsets, &self.items) {
             buf.extend_from_slice(item);
-            buf.extend_from_slice(&vec![0; buf.len().next_multiple_of(16) - buf.len()]);
-            assert_eq!(buf.len(), offset.next_multiple_of(16) as usize);
+            buf.extend_from_slice(&vec![
+                0;
+                buf.len().next_multiple_of(RKYV_ALIGNMENT) - buf.len()
+            ]);
+            assert_eq!(buf.len(), offset.next_multiple_of(RKYV_ALIGNMENT) as usize);
         }
         let (prefix, hints, postfix): (_, &[u32], _) = unsafe { buf.align_to() };
         assert_eq!(prefix, &[]);