diff --git a/Signal/src/util/OWSBackupExportJob.m b/Signal/src/util/OWSBackupExportJob.m
index 56cda6d6b..662d83ab6 100644
--- a/Signal/src/util/OWSBackupExportJob.m
+++ b/Signal/src/util/OWSBackupExportJob.m
@@ -817,6 +817,7 @@ NS_ASSUME_NONNULL_BEGIN
                 backupFragment.recordName = recordName;
                 backupFragment.encryptionKey = exportItem.encryptedItem.encryptionKey;
                 backupFragment.relativeFilePath = attachmentExport.relativeFilePath;
+                backupFragment.attachmentId = attachmentExport.attachmentId;
                 backupFragment.uncompressedDataLength = exportItem.uncompressedDataLength;
                 [backupFragment save];
 
@@ -923,6 +924,10 @@ NS_ASSUME_NONNULL_BEGIN
             OWSAssert(item.attachmentExport.relativeFilePath.length > 0);
             itemJson[kOWSBackup_ManifestKey_RelativeFilePath] = item.attachmentExport.relativeFilePath;
         }
+        if (item.attachmentExport.attachmentId) {
+            OWSAssert(item.attachmentExport.attachmentId.length > 0);
+            itemJson[kOWSBackup_ManifestKey_AttachmentId] = item.attachmentExport.attachmentId;
+        }
         if (item.uncompressedDataLength) {
             itemJson[kOWSBackup_ManifestKey_DataSize] = item.uncompressedDataLength;
         }
diff --git a/Signal/src/util/OWSBackupJob.h b/Signal/src/util/OWSBackupJob.h
index 092854f3f..663ed9e5a 100644
--- a/Signal/src/util/OWSBackupJob.h
+++ b/Signal/src/util/OWSBackupJob.h
@@ -12,6 +12,7 @@ extern NSString *const kOWSBackup_ManifestKey_AttachmentFiles;
 extern NSString *const kOWSBackup_ManifestKey_RecordName;
 extern NSString *const kOWSBackup_ManifestKey_EncryptionKey;
 extern NSString *const kOWSBackup_ManifestKey_RelativeFilePath;
+extern NSString *const kOWSBackup_ManifestKey_AttachmentId;
 extern NSString *const kOWSBackup_ManifestKey_DataSize;
 
 @class OWSBackupIO;
diff --git a/Signal/src/util/OWSBackupJob.m b/Signal/src/util/OWSBackupJob.m
index 0c6cdae3b..990cf0e30 100644
--- a/Signal/src/util/OWSBackupJob.m
+++ b/Signal/src/util/OWSBackupJob.m
@@ -16,6 +16,7 @@ NSString *const kOWSBackup_ManifestKey_AttachmentFiles = @"attachment_files";
 NSString *const kOWSBackup_ManifestKey_RecordName = @"record_name";
 NSString *const kOWSBackup_ManifestKey_EncryptionKey = @"encryption_key";
 NSString *const kOWSBackup_ManifestKey_RelativeFilePath = @"relative_file_path";
+NSString *const kOWSBackup_ManifestKey_AttachmentId = @"attachment_id";
 NSString *const kOWSBackup_ManifestKey_DataSize = @"data_size";
 
 NSString *const kOWSBackup_KeychainService = @"kOWSBackup_KeychainService";
@@ -257,6 +258,7 @@ NSString *const kOWSBackup_KeychainService = @"kOWSBackup_KeychainService";
         NSString *_Nullable recordName = itemMap[kOWSBackup_ManifestKey_RecordName];
         NSString *_Nullable encryptionKeyString = itemMap[kOWSBackup_ManifestKey_EncryptionKey];
         NSString *_Nullable relativeFilePath = itemMap[kOWSBackup_ManifestKey_RelativeFilePath];
+        NSString *_Nullable attachmentId = itemMap[kOWSBackup_ManifestKey_AttachmentId];
         NSNumber *_Nullable uncompressedDataLength = itemMap[kOWSBackup_ManifestKey_DataSize];
         if (![recordName isKindOfClass:[NSString class]]) {
             OWSProdLogAndFail(@"%@ manifest has invalid recordName: %@.", self.logTag, key);
@@ -271,6 +273,11 @@ NSString *const kOWSBackup_KeychainService = @"kOWSBackup_KeychainService";
             OWSProdLogAndFail(@"%@ manifest has invalid relativeFilePath: %@.", self.logTag, key);
             return nil;
         }
+        // attachmentId is an optional field.
+        if (attachmentId && ![attachmentId isKindOfClass:[NSString class]]) {
+            OWSProdLogAndFail(@"%@ manifest has invalid attachmentId: %@.", self.logTag, key);
+            return nil;
+        }
         NSData *_Nullable encryptionKey = [NSData dataFromBase64String:encryptionKeyString];
         if (!encryptionKey) {
             OWSProdLogAndFail(@"%@ manifest has corrupt encryptionKey: %@.", self.logTag, key);
@@ -286,6 +293,7 @@ NSString *const kOWSBackup_KeychainService = @"kOWSBackup_KeychainService";
         item.recordName = recordName;
         item.encryptionKey = encryptionKey;
         item.relativeFilePath = relativeFilePath;
+        item.attachmentId = attachmentId;
         item.uncompressedDataLength = uncompressedDataLength;
         [items addObject:item];
     }
diff --git a/SignalServiceKit/src/Util/OWSBackupFragment.h b/SignalServiceKit/src/Util/OWSBackupFragment.h
index 7dece99be..6db141c00 100644
--- a/SignalServiceKit/src/Util/OWSBackupFragment.h
+++ b/SignalServiceKit/src/Util/OWSBackupFragment.h
@@ -28,6 +28,9 @@ NS_ASSUME_NONNULL_BEGIN
 // file should reside relative to the attachments folder.
 @property (nonatomic, nullable) NSString *relativeFilePath;
 
+// This property is only set for attachments.
+@property (nonatomic, nullable) NSString *attachmentId;
+
 // This property is only set if the manifest item is downloaded.
 @property (nonatomic, nullable) NSString *downloadFilePath;