diff --git a/libcrux-ml-kem/src/simd/simd256.rs b/libcrux-ml-kem/src/simd/simd256.rs
index a2ce2e36c..17ba61313 100644
--- a/libcrux-ml-kem/src/simd/simd256.rs
+++ b/libcrux-ml-kem/src/simd/simd256.rs
@@ -17,10 +17,17 @@ pub(crate) struct SIMD256Vector {
 #[allow(dead_code)]
 fn print_m256i_as_i32s(a: __m256i, prefix: String) {
     let mut a_bytes = [0i32; 8];
-    unsafe { _mm256_store_si256(a_bytes.as_mut_ptr() as *mut __m256i, a) };
+    unsafe { _mm256_storeu_si256(a_bytes.as_mut_ptr() as *mut __m256i, a) };
     println!("{}: {:?}", prefix, a_bytes);
 }
 
+#[allow(dead_code)]
+fn print_m256i_as_i64s(a: __m256i, prefix: String) {
+    let mut a_bytes = [0i64; 4];
+    unsafe { _mm256_storeu_si256(a_bytes.as_mut_ptr() as *mut __m256i, a) };
+    println!("{}: {:x?}", prefix, a_bytes);
+}
+
 #[allow(non_snake_case)]
 #[inline(always)]
 fn ZERO() -> SIMD256Vector {
@@ -158,7 +165,7 @@ fn montgomery_reduce(v: SIMD256Vector) -> SIMD256Vector {
         let t = _mm256_mullo_epi16(v.elements, inverse_of_modulus_mod_montgomery_r);
         let k_times_modulus = _mm256_mulhi_epi16(t, field_modulus);
         let value_high = _mm256_srli_epi32(v.elements, MONTGOMERY_SHIFT as i32);
-        let res =_mm256_sub_epi16(value_high, k_times_modulus);
+        let res = _mm256_sub_epi16(value_high, k_times_modulus);
         let res = _mm256_slli_epi32(res, 16);
         _mm256_srai_epi32(res, 16)
     };
@@ -423,8 +430,30 @@ fn deserialize_5(v: &[u8]) -> SIMD256Vector {
 
 #[inline(always)]
 fn serialize_10(v: SIMD256Vector) -> [u8; 10] {
-    let input = portable::PortableVector::from_i32_array(to_i32_array(v));
-    portable::PortableVector::serialize_10(input)
+    let mut out = [0u8; 16];
+
+    unsafe {
+        let shifted = _mm256_sllv_epi32(v.elements, _mm256_set_epi32(10, 0, 10, 0, 10, 0, 10, 0));
+        let shifted = _mm256_shuffle_epi32(shifted, 0b_00_11_00_01);
+
+        let bits = _mm256_add_epi32(v.elements, shifted);
+
+        let bits = _mm256_shuffle_epi32(bits, 0b_00_00_10_00);
+        let bits = _mm256_sllv_epi32(bits, _mm256_set_epi32(0, 0, 0, 12, 0, 0, 0, 12));
+        let bits = _mm256_srli_epi64(bits, 12);
+
+        let bits = _mm256_permute4x64_epi64(bits, 0b00_00_10_00);
+        let shuffle_by = _mm256_set_epi8(
+            8, 4, 3, 2, 1, 0, -1, -1, -1, -1, -1, -1, 12, 11, 10, 9, -1, -1, -1, -1, -1, -1, 12,
+            11, 10, 9, 8, 4, 3, 2, 1, 0,
+        );
+
+        let bits_sequential = _mm256_shuffle_epi8(bits, shuffle_by);
+        let bits_sequential = _mm256_castsi256_si128(bits_sequential);
+        _mm_storeu_si128(out.as_mut_ptr() as *mut __m128i, bits_sequential);
+    };
+
+    out[0..10].try_into().unwrap()
 }
 
 #[inline(always)]