diff --git a/app/src/main/java/org/thoughtcrime/securesms/attachments/ArchivedAttachment.kt b/app/src/main/java/org/thoughtcrime/securesms/attachments/ArchivedAttachment.kt
index 4c732d27a6..bda906d2a8 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/attachments/ArchivedAttachment.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/attachments/ArchivedAttachment.kt
@@ -25,8 +25,10 @@ class ArchivedAttachment : Attachment {
   constructor(
     contentType: String?,
     size: Long,
-    cdn: Cdn,
-    cdnKey: ByteArray,
+    cdn: Int,
+    key: ByteArray,
+    cdnKey: String?,
+    archiveCdn: Int?,
     archiveMediaName: String,
     archiveMediaId: String,
     digest: ByteArray,
@@ -46,9 +48,9 @@ class ArchivedAttachment : Attachment {
     transferState = AttachmentTable.TRANSFER_NEEDS_RESTORE,
     size = size,
     fileName = null,
-    cdn = cdn,
-    remoteLocation = null,
-    remoteKey = Base64.encodeWithoutPadding(cdnKey),
+    cdn = Cdn.fromCdnNumber(cdn),
+    remoteLocation = cdnKey,
+    remoteKey = Base64.encodeWithoutPadding(key),
     remoteDigest = digest,
     incrementalDigest = incrementalMac,
     fastPreflightId = null,
@@ -65,7 +67,7 @@ class ArchivedAttachment : Attachment {
     audioHash = null,
     transformProperties = null
   ) {
-    this.archiveCdn = cdn.cdnNumber
+    this.archiveCdn = archiveCdn ?: Cdn.CDN_3.cdnNumber
     this.archiveMediaName = archiveMediaName
     this.archiveMediaId = archiveMediaId
   }
diff --git a/app/src/main/java/org/thoughtcrime/securesms/backup/v2/database/ChatItemImportInserter.kt b/app/src/main/java/org/thoughtcrime/securesms/backup/v2/database/ChatItemImportInserter.kt
index 12337a2920..161fc3e9f0 100644
--- a/app/src/main/java/org/thoughtcrime/securesms/backup/v2/database/ChatItemImportInserter.kt
+++ b/app/src/main/java/org/thoughtcrime/securesms/backup/v2/database/ChatItemImportInserter.kt
@@ -618,8 +618,10 @@ class ChatItemImportInserter(
       return ArchivedAttachment(
         contentType = contentType,
         size = pointer.backupLocator.size.toLong(),
-        cdn = Cdn.fromCdnNumber(pointer.backupLocator.cdnNumber),
-        cdnKey = pointer.backupLocator.key.toByteArray(),
+        cdn = pointer.backupLocator.transitCdnNumber ?: Cdn.CDN_0.cdnNumber,
+        key = pointer.backupLocator.key.toByteArray(),
+        cdnKey = pointer.backupLocator.transitCdnKey,
+        archiveCdn = pointer.backupLocator.cdnNumber,
         archiveMediaName = pointer.backupLocator.mediaName,
         archiveMediaId = backupState.backupKey.deriveMediaId(MediaName(pointer.backupLocator.mediaName)).encode(),
         digest = pointer.backupLocator.digest.toByteArray(),
diff --git a/app/src/main/protowire/Backup.proto b/app/src/main/protowire/Backup.proto
index aa3208a861..f3a6c9213c 100644
--- a/app/src/main/protowire/Backup.proto
+++ b/app/src/main/protowire/Backup.proto
@@ -388,10 +388,16 @@ message FilePointer {
   // References attachments in the backup (media) storage tier.
   message BackupLocator {
     string mediaName = 1;
-    uint32 cdnNumber = 2;
+    // If present, the cdn number of the succesful upload.
+    // If empty/0, may still have been uploaded, and clients
+    // can discover the cdn number via the list endpoint.
+    optional uint32 cdnNumber = 2;
     bytes key = 3;
     bytes digest = 4;
     uint32 size = 5;
+    // Fallback in case backup tier upload failed.
+    optional string transitCdnKey = 6;
+    optional uint32 transitCdnNumber = 7;
   }
 
   // References attachments in the transit storage tier.