diff --git a/src/array_string.rs b/src/array_string.rs
index 90cfc09..7f6e299 100644
--- a/src/array_string.rs
+++ b/src/array_string.rs
@@ -31,10 +31,11 @@ use serde::{Serialize, Deserialize, Serializer, Deserializer};
 /// The string is a contiguous value that you can store directly on the stack
 /// if needed.
 #[derive(Copy)]
+#[repr(C)]
 pub struct ArrayString<const CAP: usize> {
     // the `len` first elements of the array are initialized
-    xs: [MaybeUninit<u8>; CAP],
     len: LenUint,
+    xs: [MaybeUninit<u8>; CAP],
 }
 
 impl<const CAP: usize> Default for ArrayString<CAP>
diff --git a/src/arrayvec.rs b/src/arrayvec.rs
index d51fbf7..6f64ba5 100644
--- a/src/arrayvec.rs
+++ b/src/arrayvec.rs
@@ -39,10 +39,11 @@ use crate::utils::MakeMaybeUninit;
 ///
 /// It offers a simple API but also dereferences to a slice, so that the full slice API is
 /// available. The ArrayVec can be converted into a by value iterator.
+#[repr(C)]
 pub struct ArrayVec<T, const CAP: usize> {
+    len: LenUint,
     // the `len` first elements of the array are initialized
     xs: [MaybeUninit<T>; CAP],
-    len: LenUint,
 }
 
 impl<T, const CAP: usize> Drop for ArrayVec<T, CAP> {