diff --git a/internal/repository/index.go b/internal/repository/index.go
index 28863436b..22528f296 100644
--- a/internal/repository/index.go
+++ b/internal/repository/index.go
@@ -294,6 +294,8 @@ func (idx *Index) EachByPack(ctx context.Context, packBlacklist restic.IDSet) <-
 					result.Blobs = append(result.Blobs, idx.toPackedBlob(e, restic.BlobType(typ)).Blob)
 				}
 			}
+			// allow GC once entry is no longer necessary
+			byPack[packID] = nil
 			select {
 			case <-ctx.Done():
 				return
diff --git a/internal/repository/index_parallel.go b/internal/repository/index_parallel.go
index dcf33113e..4fe0797af 100644
--- a/internal/repository/index_parallel.go
+++ b/internal/repository/index_parallel.go
@@ -52,6 +52,10 @@ func ForAllIndexes(ctx context.Context, repo restic.Repository,
 			var idx *Index
 			oldFormat := false
 
+			if cap(buf) < int(fi.Size) {
+				// overallocate a bit
+				buf = make([]byte, fi.Size+128*1024)
+			}
 			buf, err = repo.LoadUnpacked(ctx, restic.IndexFile, fi.ID, buf[:0])
 			if err == nil {
 				idx, oldFormat, err = DecodeIndex(buf, fi.ID)
diff --git a/internal/repository/master_index.go b/internal/repository/master_index.go
index 955080e82..05d0fdce2 100644
--- a/internal/repository/master_index.go
+++ b/internal/repository/master_index.go
@@ -150,7 +150,7 @@ func (mi *MasterIndex) Packs(packBlacklist restic.IDSet) restic.IDSet {
 	packs := restic.NewIDSet()
 	for _, idx := range mi.idx {
 		idxPacks := idx.Packs()
-		if idx.final {
+		if idx.final && len(packBlacklist) > 0 {
 			idxPacks = idxPacks.Sub(packBlacklist)
 		}
 		packs.Merge(idxPacks)
@@ -458,6 +458,8 @@ func (mi *MasterIndex) ListPacks(ctx context.Context, packs restic.IDSet) <-chan
 
 			// pass on packs
 			for packID, pbs := range packBlob {
+				// allow GC
+				packBlob[packID] = nil
 				select {
 				case out <- restic.PackBlobs{PackID: packID, Blobs: pbs}:
 				case <-ctx.Done():