diff --git a/src/handshake-xx-fallback.ts b/src/handshake-xx-fallback.ts
index 900705e..a7c0788 100644
--- a/src/handshake-xx-fallback.ts
+++ b/src/handshake-xx-fallback.ts
@@ -16,7 +16,7 @@ import { WrappedConnection } from "./noise";
 import {decode0, decode1, encode1} from "./encoder";
 
 export class Handshake extends XXHandshake {
-  private ephemeralKeys: KeyPair;
+  private ephemeralKeys?: KeyPair;
   private initialMsg: bytes;
 
   constructor(
@@ -27,12 +27,14 @@ export class Handshake extends XXHandshake {
     staticKeys: KeyPair,
     connection: WrappedConnection,
     remotePeer: PeerId,
-    ephemeralKeys: KeyPair,
     initialMsg: bytes,
+    ephemeralKeys?: KeyPair,
     handshake?: XX,
   ) {
     super(isInitiator, libp2pPrivateKey, libp2pPublicKey, prologue, staticKeys, connection, remotePeer, handshake);
-    this.ephemeralKeys = ephemeralKeys;
+    if (ephemeralKeys) {
+      this.ephemeralKeys = ephemeralKeys;
+    }
     this.initialMsg = initialMsg;
   }
 
diff --git a/src/noise.ts b/src/noise.ts
index 81656cf..249e76d 100644
--- a/src/noise.ts
+++ b/src/noise.ts
@@ -130,7 +130,7 @@ export class Noise implements NoiseConnection {
   ): Promise<XXFallback> {
     const { isInitiator, libp2pPublicKey, remotePeer, connection } = params;
     const handshake =
-      new XXFallback(isInitiator, this.privateKey, libp2pPublicKey, this.prologue, this.staticKeys, connection, remotePeer, ephemeralKeys, initialMsg);
+      new XXFallback(isInitiator, this.privateKey, libp2pPublicKey, this.prologue, this.staticKeys, connection, remotePeer, initialMsg, ephemeralKeys);
 
     try {
       await handshake.propose();
diff --git a/test/xx-fallback-handshake.test.ts b/test/xx-fallback-handshake.test.ts
index 130a8ff..7eb7e28 100644
--- a/test/xx-fallback-handshake.test.ts
+++ b/test/xx-fallback-handshake.test.ts
@@ -48,10 +48,10 @@ describe("XX Fallback Handshake", () => {
       });
 
       const handshakeInit =
-        new Handshake(true, initiatorPrivKey, initiatorPubKey, prologue, staticKeysInitiator, connectionFrom, peerB, ephemeralKeys, initialMsg);
+        new Handshake(true, initiatorPrivKey, initiatorPubKey, prologue, staticKeysInitiator, connectionFrom, peerB, initialMsg, ephemeralKeys);
 
       const handshakeResp =
-        new Handshake(false, responderPrivKey, responderPubKey, prologue, staticKeysResponder, connectionTo, peerA, ephemeralKeys, initialMsg);
+        new Handshake(false, responderPrivKey, responderPubKey, prologue, staticKeysResponder, connectionTo, peerA, initialMsg);
 
 
       await handshakeInit.propose();