diff --git a/src/fields.rs b/src/fields.rs
index 70ce865..9e01217 100644
--- a/src/fields.rs
+++ b/src/fields.rs
@@ -11,6 +11,6 @@ pub use fq::*;
 fn u64_to_u32(limbs: &[u64]) -> alloc::vec::Vec<u32> {
     limbs
         .iter()
-        .flat_map(|limb| alloc::vec![(limb & 0xFFFF_FFFF) as u32, (limb >> 32) as u32])
+        .flat_map(|limb| Some((limb & 0xFFFF_FFFF) as u32).into_iter().chain(Some((limb >> 32) as u32)))
         .collect()
 }