diff --git a/Cargo.toml b/Cargo.toml
index 6a45270..026111a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "arrayvec"
-version = "0.4.9"
+version = "0.4.10"
 authors = ["bluss"]
 license = "MIT/Apache-2.0"
 
diff --git a/README.rst b/README.rst
index 29d3a2f..4af5330 100644
--- a/README.rst
+++ b/README.rst
@@ -22,6 +22,11 @@ __ https://docs.rs/arrayvec
 Recent Changes (arrayvec)
 -------------------------
 
+- 0.4.10
+
+  - Use ``repr(C)`` in the ``union`` version that was introduced in 0.4.9, to
+    allay some soundness concerns.
+
 - 0.4.9
 
   - Use ``union`` in the implementation on when this is detected to be supported
diff --git a/src/maybe_uninit.rs b/src/maybe_uninit.rs
index 71ec8f0..9ed1f6a 100644
--- a/src/maybe_uninit.rs
+++ b/src/maybe_uninit.rs
@@ -6,18 +6,13 @@ use std::mem::ManuallyDrop;
 /// A combination of ManuallyDrop and “maybe uninitialized”;
 /// this wraps a value that can be wholly or partially uninitialized;
 /// it also has no drop regardless of the type of T.
-#[derive(Copy)]
+#[repr(C)] // for cast from self ptr to value
 pub union MaybeUninit<T> {
     empty: (),
     value: ManuallyDrop<T>,
 }
 // Why we don't use std's MaybeUninit on nightly? See the ptr method
 
-impl<T> Clone for MaybeUninit<T> where T: Copy
-{
-    fn clone(&self) -> Self { *self }
-}
-
 impl<T> MaybeUninit<T> {
     /// Create a new MaybeUninit with uninitialized interior
     pub unsafe fn uninitialized() -> Self {