diff --git a/src/openpgp.js b/src/openpgp.js
index 8fb07ef8..4c671583 100644
--- a/src/openpgp.js
+++ b/src/openpgp.js
@@ -629,7 +629,7 @@ async function convertStream(data, streaming) {
  * @returns {Object}                       the data in the respective format
  */
 async function convertStreams(obj, streaming, keys=[]) {
-  if (Object.prototype.isPrototypeOf(obj)) {
+  if (Object.prototype.isPrototypeOf(obj) && !Uint8Array.prototype.isPrototypeOf(obj)) {
     await Promise.all(Object.entries(obj).map(async ([key, value]) => { // recursively search all children
       if (util.isStream(value) || keys.includes(key)) {
         obj[key] = await convertStream(value, streaming);
diff --git a/src/util.js b/src/util.js
index 495a6260..e2eff20d 100644
--- a/src/util.js
+++ b/src/util.js
@@ -102,7 +102,7 @@ export default {
    * @returns {Object}
    */
   restoreStreams: function(obj) {
-    if (Object.prototype.isPrototypeOf(obj)) {
+    if (Object.prototype.isPrototypeOf(obj) && !Uint8Array.prototype.isPrototypeOf(obj)) {
       Object.entries(obj).forEach(([key, value]) => { // recursively search all children
         if (MessagePort.prototype.isPrototypeOf(value)) {
           obj[key] = new ReadableStream({