diff --git a/src/matrix/e2ee/attachment.js b/src/matrix/e2ee/attachment.js
index 105c16c5..3ead83eb 100644
--- a/src/matrix/e2ee/attachment.js
+++ b/src/matrix/e2ee/attachment.js
@@ -65,7 +65,7 @@ export async function encryptAttachment(platform, blob) {
     const ciphertext = await crypto.aes.encryptCTR({jwkKey: key, iv, data: buffer});
     const digest = await crypto.digest("SHA-256", ciphertext);
     return {
-        blob: platform.createBlob(ciphertext, blob.mimeType),
+        blob: platform.createBlob(ciphertext, 'application/octet-stream'),
         info: {
             v: "v2",
             key,
diff --git a/src/matrix/room/AttachmentUpload.js b/src/matrix/room/AttachmentUpload.js
index 5dd957a0..356bb5a7 100644
--- a/src/matrix/room/AttachmentUpload.js
+++ b/src/matrix/room/AttachmentUpload.js
@@ -98,10 +98,10 @@ export class AttachmentUpload {
         }
         let prefix = urlPath.substr(0, urlPath.lastIndexOf("url"));
         setPath(`${prefix}info.size`, content, this._transferredBlob.size);
-        setPath(`${prefix}info.mimetype`, content, this._unencryptedBlob.mimeType);
+        setPath(`${prefix}info.mimetype`, content, this._transferredBlob.mimeType);
         if (this._isEncrypted) {
             setPath(`${prefix}file`, content, Object.assign(this._encryptionInfo, {
-                mimetype: this._unencryptedBlob.mimeType,
+                mimetype: this._transferredBlob.mimeType,
                 url: this._mxcUrl
             }));
         } else {