diff --git a/ts/session/messages/outgoing/content/data/ExpirationTimerUpdateMessage.ts b/ts/session/messages/outgoing/content/data/ExpirationTimerUpdateMessage.ts
index 2da6fc6b3..88eb245f4 100644
--- a/ts/session/messages/outgoing/content/data/ExpirationTimerUpdateMessage.ts
+++ b/ts/session/messages/outgoing/content/data/ExpirationTimerUpdateMessage.ts
@@ -37,9 +37,13 @@ export class ExpirationTimerUpdateMessage extends DataMessage {
 
     if (this.groupId) {
       const groupMessage = new SignalService.GroupContext();
-      groupMessage.id = new Uint8Array(
-        StringUtils.encode(this.groupId.key, 'utf8')
-      );
+      let groupIdWithPrefix: string = this.groupId.key;
+      if (!this.groupId.key.startsWith(PubKey.PREFIX_GROUP_TEXTSECURE)) {
+        groupIdWithPrefix = PubKey.PREFIX_GROUP_TEXTSECURE + this.groupId.key;
+      }
+      const encoded = StringUtils.encode(groupIdWithPrefix, 'utf8');
+      const id = new Uint8Array(encoded);
+      groupMessage.id = id;
       groupMessage.type = SignalService.GroupContext.Type.DELIVER;
 
       data.group = groupMessage;