diff --git a/ssh/agent/client.go b/ssh/agent/client.go
index 3c4d18a..eb6bc71 100644
--- a/ssh/agent/client.go
+++ b/ssh/agent/client.go
@@ -226,7 +226,9 @@ var ErrExtensionUnsupported = errors.New("agent: extension unsupported")
 
 type extensionAgentMsg struct {
 	ExtensionType string `sshtype:"27"`
-	Contents      []byte
+	// NOTE: this matches OpenSSH's PROTOCOL.agent, not the IETF draft [PROTOCOL.agent],
+	// so that it matches what OpenSSH actually implements in the wild.
+	Contents []byte `ssh:"rest"`
 }
 
 // Key represents a protocol 2 public key as defined in