diff --git a/ts/services/backups/export.preload.ts b/ts/services/backups/export.preload.ts
index 7bcfdb151b..158c9887fa 100644
--- a/ts/services/backups/export.preload.ts
+++ b/ts/services/backups/export.preload.ts
@@ -1612,9 +1612,25 @@ export class BackupExportStream extends Readable {
       );
     } else if (message.source) {
       authorId = this.#getRecipientByE164(message.source, 'message.source');
+    } else if (isIncoming) {
+      if (conversation && isDirectConversation(conversation.attributes)) {
+        authorId = this.#getRecipientByConversationId(
+          conversation.id,
+          'message-missing-source'
+        );
+      }
+      if (authorId != null) {
+        log.warn(
+          `${message.sent_at}: Incoming message in group missing source, using conversation`
+        );
+      } else {
+        log.warn(
+          `${message.sent_at}: Incoming message in group or unknown conversation` +
+            ' without source, dropping'
+        );
+        return undefined;
+      }
     } else {
-      strictAssert(!isIncoming, 'Incoming message must have source');
-
       // Author must be always present, even if we are directionless
       authorId = me;
     }
diff --git a/ts/test-electron/backup/bubble_test.preload.ts b/ts/test-electron/backup/bubble_test.preload.ts
index fe8e655ea9..75ae9dd83f 100644
--- a/ts/test-electron/backup/bubble_test.preload.ts
+++ b/ts/test-electron/backup/bubble_test.preload.ts
@@ -387,6 +387,63 @@ describe('backup/bubble messages', () => {
     );
   });
 
+  it('fixes source-missing incoming 1:1 messages', async () => {
+    await asymmetricRoundtripHarness(
+      [
+        {
+          conversationId: contactA.id,
+          id: generateGuid(),
+          type: 'incoming',
+          received_at: 3,
+          received_at_ms: 3,
+          sent_at: 3,
+          readStatus: ReadStatus.Unread,
+          seenStatus: SeenStatus.Unseen,
+          unidentifiedDeliveryReceived: true,
+          timestamp: 3,
+          body: 'hello',
+        },
+      ],
+      [
+        {
+          conversationId: contactA.id,
+          id: generateGuid(),
+          type: 'incoming',
+          received_at: 3,
+          received_at_ms: 3,
+          sent_at: 3,
+          sourceServiceId: CONTACT_A,
+          readStatus: ReadStatus.Unread,
+          seenStatus: SeenStatus.Unseen,
+          unidentifiedDeliveryReceived: true,
+          timestamp: 3,
+          body: 'hello',
+        },
+      ]
+    );
+  });
+
+  it('drops source-missing incoming group messages', async () => {
+    await asymmetricRoundtripHarness(
+      [
+        {
+          conversationId: gv2.id,
+          id: generateGuid(),
+          type: 'incoming',
+          received_at: 3,
+          received_at_ms: 3,
+          sent_at: 3,
+          readStatus: ReadStatus.Unread,
+          seenStatus: SeenStatus.Unseen,
+          unidentifiedDeliveryReceived: true,
+          timestamp: 3,
+          body: 'hello',
+        },
+      ],
+      []
+    );
+  });
+
   it('drops misattributed incoming 1:1 messages', async () => {
     await asymmetricRoundtripHarness(
       [