diff --git a/html5/js/Protocol.js b/html5/js/Protocol.js
index 842f5870..7f25bf19 100644
--- a/html5/js/Protocol.js
+++ b/html5/js/Protocol.js
@@ -462,7 +462,7 @@ class XpraProtocol {
       if (this.cipher_out_key) {
         //console("encrypting", packet[0], "packet using", JSON.stringify(this.cipher_out_params), ":", bdata);
         crypto.subtle.encrypt(this.cipher_out_params, this.cipher_out_key, bdata)
-        .then(encrypted => this.send_packet(encrypted, payload_size, true))
+        .then(encrypted => this.send_packet(new Uint8Array(encrypted), payload_size, true))
         .catch(err => this.protocol_error("failed to encrypt packet: "+err));
         return;
       }