diff --git a/src/ed25519.rs b/src/ed25519.rs
index cd9afcf..2844923 100644
--- a/src/ed25519.rs
+++ b/src/ed25519.rs
@@ -753,6 +753,7 @@ impl<'d> Deserialize<'d> for PublicKey {
 
 /// An ed25519 keypair.
 #[derive(Debug)]
+#[repr(C)]
 pub struct Keypair {
     /// The secret half of this keypair.
     pub secret: SecretKey,