diff --git a/internal/repository/index_test.go b/internal/repository/index_test.go
index c96101906..513f4c5d1 100644
--- a/internal/repository/index_test.go
+++ b/internal/repository/index_test.go
@@ -3,6 +3,7 @@ package repository_test
 import (
 	"bytes"
 	"math/rand"
+	"sync"
 	"testing"
 
 	"github.com/restic/restic/internal/repository"
@@ -329,15 +330,40 @@ func TestIndexUnserialize(t *testing.T) {
 	}
 }
 
+var (
+	benchmarkIndexJSON     []byte
+	benchmarkIndexJSONOnce sync.Once
+)
+
+func initBenchmarkIndexJSON() {
+	idx, _ := createRandomIndex(rand.New(rand.NewSource(0)))
+	var buf bytes.Buffer
+	idx.Encode(&buf)
+	benchmarkIndexJSON = buf.Bytes()
+}
+
 func BenchmarkDecodeIndex(b *testing.B) {
+	benchmarkIndexJSONOnce.Do(initBenchmarkIndexJSON)
 	b.ResetTimer()
 
 	for i := 0; i < b.N; i++ {
-		_, err := repository.DecodeIndex(docExample)
+		_, err := repository.DecodeIndex(benchmarkIndexJSON)
 		rtest.OK(b, err)
 	}
 }
 
+func BenchmarkDecodeIndexParallel(b *testing.B) {
+	benchmarkIndexJSONOnce.Do(initBenchmarkIndexJSON)
+	b.ResetTimer()
+
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			_, err := repository.DecodeIndex(benchmarkIndexJSON)
+			rtest.OK(b, err)
+		}
+	})
+}
+
 func TestIndexUnserializeOld(t *testing.T) {
 	idx, err := repository.DecodeOldIndex(docOldExample)
 	rtest.OK(t, err)
@@ -401,7 +427,7 @@ func createRandomIndex(rng *rand.Rand) (idx *repository.Index, lookupID restic.I
 		var blobs []restic.Blob
 		offset := 0
 		for offset < maxPackSize {
-			size := 2000 + rand.Intn(4*1024*1024)
+			size := 2000 + rng.Intn(4*1024*1024)
 			id := NewRandomTestID(rng)
 			blobs = append(blobs, restic.Blob{
 				Type:   restic.DataBlob,
@@ -411,12 +437,12 @@ func createRandomIndex(rng *rand.Rand) (idx *repository.Index, lookupID restic.I
 			})
 
 			offset += size
-
-			if rand.Float32() < 0.001 && lookupID.IsNull() {
-				lookupID = id
-			}
 		}
 		idx.StorePack(packID, blobs)
+
+		if i == 0 {
+			lookupID = blobs[rng.Intn(len(blobs))].ID
+		}
 	}
 
 	return idx, lookupID
@@ -444,12 +470,25 @@ func BenchmarkIndexHasKnown(b *testing.B) {
 }
 
 func BenchmarkIndexAlloc(b *testing.B) {
+	rng := rand.New(rand.NewSource(0))
 	b.ReportAllocs()
+
 	for i := 0; i < b.N; i++ {
-		createRandomIndex(rand.New(rand.NewSource(0)))
+		createRandomIndex(rng)
 	}
 }
 
+func BenchmarkIndexAllocParallel(b *testing.B) {
+	b.ReportAllocs()
+
+	b.RunParallel(func(pb *testing.PB) {
+		rng := rand.New(rand.NewSource(0))
+		for pb.Next() {
+			createRandomIndex(rng)
+		}
+	})
+}
+
 func TestIndexHas(t *testing.T) {
 	type testEntry struct {
 		id             restic.ID
diff --git a/internal/repository/master_index_test.go b/internal/repository/master_index_test.go
index 7dfcdda5f..3b858253a 100644
--- a/internal/repository/master_index_test.go
+++ b/internal/repository/master_index_test.go
@@ -1,6 +1,7 @@
 package repository_test
 
 import (
+	"fmt"
 	"math/rand"
 	"testing"
 
@@ -74,11 +75,11 @@ func BenchmarkMasterIndexLookupMultipleIndex(b *testing.B) {
 	mIdx := repository.NewMasterIndex()
 
 	for i := 0; i < 5; i++ {
-		idx, _ := createRandomIndex(rand.New(rng))
+		idx, _ := createRandomIndex(rng)
 		mIdx.Insert(idx)
 	}
 
-	idx1, lookupID := createRandomIndex(rand.New(rng))
+	idx1, lookupID := createRandomIndex(rng)
 	mIdx.Insert(idx1)
 
 	b.ResetTimer()
@@ -107,17 +108,51 @@ func BenchmarkMasterIndexLookupMultipleIndexUnknown(b *testing.B) {
 	lookupID := restic.NewRandomID()
 	mIdx := repository.NewMasterIndex()
 
-	for i := 0; i < 5; i++ {
-		idx, _ := createRandomIndex(rand.New(rng))
+	for i := 0; i < 6; i++ {
+		idx, _ := createRandomIndex(rng)
 		mIdx.Insert(idx)
 	}
 
-	idx1, _ := createRandomIndex(rand.New(rng))
-	mIdx.Insert(idx1)
-
 	b.ResetTimer()
 
 	for i := 0; i < b.N; i++ {
 		mIdx.Lookup(lookupID, restic.DataBlob)
 	}
 }
+
+func BenchmarkMasterIndexLookupParallel(b *testing.B) {
+	mIdx := repository.NewMasterIndex()
+
+	for _, numindices := range []int{5, 10, 20} {
+		var lookupID restic.ID
+
+		b.StopTimer()
+		rng := rand.New(rand.NewSource(0))
+		for i := 0; i < numindices; i++ {
+			var idx *repository.Index
+			idx, lookupID = createRandomIndex(rng)
+			mIdx.Insert(idx)
+		}
+		b.StartTimer()
+
+		name := fmt.Sprintf("known,indices=%d", numindices)
+		b.Run(name, func(b *testing.B) {
+			b.RunParallel(func(pb *testing.PB) {
+				for pb.Next() {
+					mIdx.Lookup(lookupID, restic.DataBlob)
+				}
+			})
+		})
+
+		lookupID = restic.NewRandomID()
+		name = fmt.Sprintf("unknown,indices=%d", numindices)
+		b.Run(name, func(b *testing.B) {
+			b.RunParallel(func(pb *testing.PB) {
+				for pb.Next() {
+					mIdx.Lookup(lookupID, restic.DataBlob)
+				}
+			})
+		})
+
+	}
+}