diff --git a/internal/archiver/blob_saver_test.go b/internal/archiver/blob_saver_test.go
index caa1e7c39..367b7be8b 100644
--- a/internal/archiver/blob_saver_test.go
+++ b/internal/archiver/blob_saver_test.go
@@ -48,14 +48,19 @@ func TestBlobSaver(t *testing.T) {
 
 	var wait sync.WaitGroup
 	var results []SaveBlobResponse
+	var lock sync.Mutex
 
 	wait.Add(20)
 	for i := 0; i < 20; i++ {
 		buf := &Buffer{Data: []byte(fmt.Sprintf("foo%d", i))}
 		idx := i
+		lock.Lock()
 		results = append(results, SaveBlobResponse{})
+		lock.Unlock()
 		b.Save(ctx, restic.DataBlob, buf, func(res SaveBlobResponse) {
+			lock.Lock()
 			results[idx] = res
+			lock.Unlock()
 			wait.Done()
 		})
 	}
diff --git a/internal/archiver/file_saver.go b/internal/archiver/file_saver.go
index 346bf736e..0742c8b57 100644
--- a/internal/archiver/file_saver.go
+++ b/internal/archiver/file_saver.go
@@ -199,7 +199,10 @@ func (s *FileSaver) saveFile(ctx context.Context, chnker *chunker.Chunker, snPat
 
 		// add a place to store the saveBlob result
 		pos := idx
+
+		lock.Lock()
 		node.Content = append(node.Content, restic.ID{})
+		lock.Unlock()
 
 		s.saveBlob(ctx, restic.DataBlob, buf, func(sbr SaveBlobResponse) {
 			lock.Lock()