diff --git a/cmd/restic/cmd_prune.go b/cmd/restic/cmd_prune.go
index 76801dea4..ad306858b 100644
--- a/cmd/restic/cmd_prune.go
+++ b/cmd/restic/cmd_prune.go
@@ -596,10 +596,8 @@ func prune(opts PruneOptions, gopts GlobalOptions, repo restic.Repository, usedB
 func writeIndexFiles(gopts GlobalOptions, repo restic.Repository, removePacks restic.IDSet, extraObsolete restic.IDs) (restic.IDSet, error) {
 	Verbosef("rebuilding index\n")
 
-	idx := (repo.Index()).(*repository.MasterIndex)
-	packcount := uint64(len(idx.Packs(removePacks)))
-	bar := newProgressMax(!gopts.Quiet, packcount, "packs processed")
-	obsoleteIndexes, err := idx.Save(gopts.ctx, repo, removePacks, extraObsolete, bar)
+	bar := newProgressMax(!gopts.Quiet, 0, "packs processed")
+	obsoleteIndexes, err := repo.Index().Save(gopts.ctx, repo, removePacks, extraObsolete, bar)
 	bar.Done()
 	return obsoleteIndexes, err
 }
diff --git a/internal/repository/master_index.go b/internal/repository/master_index.go
index f52060d51..171411bf4 100644
--- a/internal/repository/master_index.go
+++ b/internal/repository/master_index.go
@@ -321,7 +321,9 @@ const saveIndexParallelism = 4
 // The new index contains the IDs of all known indexes in the "supersedes"
 // field. The IDs are also returned in the IDSet obsolete.
 // After calling this function, you should remove the obsolete index files.
-func (mi *MasterIndex) Save(ctx context.Context, repo restic.Repository, packBlacklist restic.IDSet, extraObsolete restic.IDs, p *progress.Counter) (obsolete restic.IDSet, err error) {
+func (mi *MasterIndex) Save(ctx context.Context, repo restic.SaverUnpacked, packBlacklist restic.IDSet, extraObsolete restic.IDs, p *progress.Counter) (obsolete restic.IDSet, err error) {
+	p.SetMax(uint64(len(mi.Packs(packBlacklist))))
+
 	mi.idxMutex.Lock()
 	defer mi.idxMutex.Unlock()
 
diff --git a/internal/repository/master_index_test.go b/internal/repository/master_index_test.go
index 79932af07..c393382c3 100644
--- a/internal/repository/master_index_test.go
+++ b/internal/repository/master_index_test.go
@@ -291,14 +291,12 @@ func BenchmarkMasterIndexLookupMultipleIndexUnknown(b *testing.B) {
 }
 
 func BenchmarkMasterIndexLookupParallel(b *testing.B) {
-	mIdx := repository.NewMasterIndex()
-
 	for _, numindices := range []int{25, 50, 100} {
 		var lookupBh restic.BlobHandle
 
 		b.StopTimer()
 		rng := rand.New(rand.NewSource(0))
-		mIdx, lookupBh = createRandomMasterIndex(b, rng, numindices, 10000)
+		mIdx, lookupBh := createRandomMasterIndex(b, rng, numindices, 10000)
 		b.StartTimer()
 
 		name := fmt.Sprintf("known,indices=%d", numindices)
@@ -361,7 +359,7 @@ func testIndexSave(t *testing.T, version uint) {
 		t.Fatal(err)
 	}
 
-	obsoletes, err := repo.Index().(*repository.MasterIndex).Save(context.TODO(), repo, nil, nil, nil)
+	obsoletes, err := repo.Index().Save(context.TODO(), repo, nil, nil, nil)
 	if err != nil {
 		t.Fatalf("unable to save new index: %v", err)
 	}
diff --git a/internal/repository/repack_test.go b/internal/repository/repack_test.go
index 8106a2f0c..f8e375a52 100644
--- a/internal/repository/repack_test.go
+++ b/internal/repository/repack_test.go
@@ -192,9 +192,7 @@ func rebuildIndex(t *testing.T, repo restic.Repository) {
 		t.Fatal(err)
 	}
 
-	_, err = (repo.Index()).(*repository.MasterIndex).
-		Save(context.TODO(), repo, restic.NewIDSet(), nil, nil)
-
+	_, err = repo.Index().Save(context.TODO(), repo, restic.NewIDSet(), nil, nil)
 	if err != nil {
 		t.Fatal(err)
 	}
diff --git a/internal/restic/repository.go b/internal/restic/repository.go
index 0d608e9bf..0e388bb5d 100644
--- a/internal/restic/repository.go
+++ b/internal/restic/repository.go
@@ -4,6 +4,7 @@ import (
 	"context"
 
 	"github.com/restic/restic/internal/crypto"
+	"github.com/restic/restic/internal/ui/progress"
 )
 
 // Repository stores data in a backend. It provides high-level functions and
@@ -82,4 +83,6 @@ type MasterIndex interface {
 	// blocks any modification of the index.
 	Each(ctx context.Context) <-chan PackedBlob
 	ListPacks(ctx context.Context, packs IDSet) <-chan PackBlobs
+
+	Save(ctx context.Context, repo SaverUnpacked, packBlacklist IDSet, extraObsolete IDs, p *progress.Counter) (obsolete IDSet, err error)
 }