diff --git a/protos/SignalService.proto b/protos/SignalService.proto
index 54391519f..f7b76be2f 100644
--- a/protos/SignalService.proto
+++ b/protos/SignalService.proto
@@ -42,7 +42,7 @@ message Content {
 
 message MediumGroupCiphertext {
   optional bytes ciphertext = 1;
-  optional string source = 2;
+  optional bytes source = 2;
   optional uint32 keyIdx = 3;
 }
 
diff --git a/ts/receiver/contentMessage.ts b/ts/receiver/contentMessage.ts
index 4425a528c..7c125267c 100644
--- a/ts/receiver/contentMessage.ts
+++ b/ts/receiver/contentMessage.ts
@@ -71,8 +71,8 @@ async function decryptForMediumGroup(
     new Uint8Array(mediumGroupCiphertext)
   );
   const ourNumber = (await UserUtil.getCurrentDevicePubKey()) as string;
-
-  if (source === ourNumber) {
+  const sourceAsStr = StringUtils.decode(source, 'hex');
+  if (sourceAsStr === ourNumber) {
     window.console.info(
       'Dropping message from ourself after decryptForMediumGroup'
     );
@@ -83,7 +83,7 @@ async function decryptForMediumGroup(
     ciphertext,
     keyIdx,
     groupId,
-    source
+    sourceAsStr
   );
 
   return plaintext;
diff --git a/ts/session/crypto/MessageEncrypter.ts b/ts/session/crypto/MessageEncrypter.ts
index ba97ca7a2..3380cb205 100644
--- a/ts/session/crypto/MessageEncrypter.ts
+++ b/ts/session/crypto/MessageEncrypter.ts
@@ -4,6 +4,7 @@ import { UserUtil } from '../../util';
 import { CipherTextObject } from '../../../libtextsecure/libsignal-protocol';
 import { encryptWithSenderKey } from '../../session/medium_group/ratchet';
 import { PubKey } from '../types';
+import { StringUtils } from '../utils';
 
 /**
  * Add padding to a message buffer
@@ -90,7 +91,7 @@ export async function encryptForMediumGroup(
   // We should include ciphertext idx in the message
   const content = SignalService.MediumGroupCiphertext.encode({
     ciphertext,
-    source: ourKey,
+    source: new Uint8Array(StringUtils.encode(ourKey, 'hex')),
     keyIdx,
   }).finish();