diff --git a/src/ed25519.rs b/src/ed25519.rs
index b01077b..57b5dcb 100644
--- a/src/ed25519.rs
+++ b/src/ed25519.rs
@@ -910,7 +910,9 @@ impl<'d> Deserialize<'d> for Keypair {
             type Value = Keypair;
 
             fn expecting(&self, formatter: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
-                formatter.write_str("An ed25519 signature as specified in RFC8032")
+                formatter.write_str("An ed25519 keypair, 64 bytes in total where the secret key is \
+                                     the first 32 bytes and is in unexpanded form, and the second \
+                                     32 bytes is a compressed point for a public key.")
             }
 
             fn visit_bytes<E>(self, bytes: &[u8]) -> Result<Keypair, E> where E: SerdeError {