diff --git a/cmd/restic/cmd_check.go b/cmd/restic/cmd_check.go
index dcf7f27df..e8596ae33 100644
--- a/cmd/restic/cmd_check.go
+++ b/cmd/restic/cmd_check.go
@@ -245,17 +245,12 @@ func runCheck(ctx context.Context, opts CheckOptions, gopts GlobalOptions, args
 
 	errorsFound := false
 	suggestIndexRebuild := false
-	suggestLegacyIndexRebuild := false
 	mixedFound := false
 	for _, hint := range hints {
 		switch hint.(type) {
 		case *checker.ErrDuplicatePacks:
 			term.Print(hint.Error())
 			suggestIndexRebuild = true
-		case *checker.ErrOldIndexFormat:
-			printer.E("error: %v\n", hint)
-			suggestLegacyIndexRebuild = true
-			errorsFound = true
 		case *checker.ErrMixedPack:
 			term.Print(hint.Error())
 			mixedFound = true
@@ -268,9 +263,6 @@ func runCheck(ctx context.Context, opts CheckOptions, gopts GlobalOptions, args
 	if suggestIndexRebuild {
 		term.Print("Duplicate packs are non-critical, you can run `restic repair index' to correct this.\n")
 	}
-	if suggestLegacyIndexRebuild {
-		printer.E("error: Found indexes using the legacy format, you must run `restic repair index' to correct this.\n")
-	}
 	if mixedFound {
 		term.Print("Mixed packs with tree and data blobs are non-critical, you can run `restic prune` to correct this.\n")
 	}
diff --git a/cmd/restic/cmd_debug.go b/cmd/restic/cmd_debug.go
index b92192492..4ce17f899 100644
--- a/cmd/restic/cmd_debug.go
+++ b/cmd/restic/cmd_debug.go
@@ -143,7 +143,7 @@ func printPacks(ctx context.Context, repo *repository.Repository, wr io.Writer)
 }
 
 func dumpIndexes(ctx context.Context, repo restic.ListerLoaderUnpacked, wr io.Writer) error {
-	return index.ForAllIndexes(ctx, repo, repo, func(id restic.ID, idx *index.Index, oldFormat bool, err error) error {
+	return index.ForAllIndexes(ctx, repo, repo, func(id restic.ID, idx *index.Index, err error) error {
 		Printf("index_id: %v\n", id)
 		if err != nil {
 			return err
diff --git a/cmd/restic/cmd_list.go b/cmd/restic/cmd_list.go
index 1a4791e31..f6c07d66f 100644
--- a/cmd/restic/cmd_list.go
+++ b/cmd/restic/cmd_list.go
@@ -60,7 +60,7 @@ func runList(ctx context.Context, gopts GlobalOptions, args []string) error {
 	case "locks":
 		t = restic.LockFile
 	case "blobs":
-		return index.ForAllIndexes(ctx, repo, repo, func(_ restic.ID, idx *index.Index, _ bool, err error) error {
+		return index.ForAllIndexes(ctx, repo, repo, func(_ restic.ID, idx *index.Index, err error) error {
 			if err != nil {
 				return err
 			}
diff --git a/internal/checker/checker.go b/internal/checker/checker.go
index 031e13807..e0c1766d7 100644
--- a/internal/checker/checker.go
+++ b/internal/checker/checker.go
@@ -75,16 +75,6 @@ func (e *ErrMixedPack) Error() string {
 	return fmt.Sprintf("pack %v contains a mix of tree and data blobs", e.PackID.Str())
 }
 
-// ErrOldIndexFormat is returned when an index with the old format is
-// found.
-type ErrOldIndexFormat struct {
-	restic.ID
-}
-
-func (err *ErrOldIndexFormat) Error() string {
-	return fmt.Sprintf("index %v has old format", err.ID)
-}
-
 func (c *Checker) LoadSnapshots(ctx context.Context) error {
 	var err error
 	c.snapshots, err = restic.MemorizeList(ctx, c.repo, restic.SnapshotFile)
@@ -112,14 +102,8 @@ func (c *Checker) LoadIndex(ctx context.Context, p *progress.Counter) (hints []e
 	debug.Log("Start")
 
 	packToIndex := make(map[restic.ID]restic.IDSet)
-	err := c.masterIndex.Load(ctx, c.repo, p, func(id restic.ID, idx *index.Index, oldFormat bool, err error) error {
+	err := c.masterIndex.Load(ctx, c.repo, p, func(id restic.ID, idx *index.Index, err error) error {
 		debug.Log("process index %v, err %v", id, err)
-
-		if oldFormat {
-			debug.Log("index %v has old format", id)
-			hints = append(hints, &ErrOldIndexFormat{id})
-		}
-
 		err = errors.Wrapf(err, "error loading index %v", id)
 
 		if err != nil {
diff --git a/internal/feature/registry.go b/internal/feature/registry.go
index 6b8f6b397..8bdb5480e 100644
--- a/internal/feature/registry.go
+++ b/internal/feature/registry.go
@@ -6,7 +6,6 @@ var Flag = New()
 // flag names are written in kebab-case
 const (
 	BackendErrorRedesign    FlagName = "backend-error-redesign"
-	DeprecateLegacyIndex    FlagName = "deprecate-legacy-index"
 	DeprecateS3LegacyLayout FlagName = "deprecate-s3-legacy-layout"
 	DeviceIDForHardlinks    FlagName = "device-id-for-hardlinks"
 	ExplicitS3AnonymousAuth FlagName = "explicit-s3-anonymous-auth"
@@ -16,7 +15,6 @@ const (
 func init() {
 	Flag.SetFlags(map[FlagName]FlagDesc{
 		BackendErrorRedesign:    {Type: Beta, Description: "enforce timeouts for stuck HTTP requests and use new backend error handling design."},
-		DeprecateLegacyIndex:    {Type: Beta, Description: "disable support for index format used by restic 0.1.0. Use `restic repair index` to update the index if necessary."},
 		DeprecateS3LegacyLayout: {Type: Beta, Description: "disable support for S3 legacy layout used up to restic 0.7.0. Use `RESTIC_FEATURES=deprecate-s3-legacy-layout=false restic migrate s3_layout` to migrate your S3 repository if necessary."},
 		DeviceIDForHardlinks:    {Type: Alpha, Description: "store deviceID only for hardlinks to reduce metadata changes for example when using btrfs subvolumes. Will be removed in a future restic version after repository format 3 is available"},
 		ExplicitS3AnonymousAuth: {Type: Beta, Description: "forbid anonymous S3 authentication unless `-o s3.unsafe-anonymous-auth=true` is set"},
diff --git a/internal/repository/index/index.go b/internal/repository/index/index.go
index 36ac2560f..14e4543bd 100644
--- a/internal/repository/index/index.go
+++ b/internal/repository/index/index.go
@@ -4,7 +4,6 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
-	"fmt"
 	"io"
 	"math"
 	"sync"
@@ -12,7 +11,6 @@ import (
 
 	"github.com/restic/restic/internal/crypto"
 	"github.com/restic/restic/internal/errors"
-	"github.com/restic/restic/internal/feature"
 	"github.com/restic/restic/internal/restic"
 
 	"github.com/restic/restic/internal/debug"
@@ -489,34 +487,15 @@ func (idx *Index) merge(idx2 *Index) error {
 	return nil
 }
 
-// isErrOldIndex returns true if the error may be caused by an old index
-// format.
-func isErrOldIndex(err error) bool {
-	e, ok := err.(*json.UnmarshalTypeError)
-	return ok && e.Value == "array"
-}
-
 // DecodeIndex unserializes an index from buf.
-func DecodeIndex(buf []byte, id restic.ID) (idx *Index, oldFormat bool, err error) {
+func DecodeIndex(buf []byte, id restic.ID) (idx *Index, err error) {
 	debug.Log("Start decoding index")
 	idxJSON := &jsonIndex{}
 
 	err = json.Unmarshal(buf, idxJSON)
 	if err != nil {
 		debug.Log("Error %v", err)
-
-		if isErrOldIndex(err) {
-			if feature.Flag.Enabled(feature.DeprecateLegacyIndex) {
-				return nil, false, fmt.Errorf("index seems to use the legacy format. update it using `restic repair index`")
-			}
-
-			debug.Log("index is probably old format, trying that")
-			idx, err = decodeOldIndex(buf)
-			idx.ids = append(idx.ids, id)
-			return idx, err == nil, err
-		}
-
-		return nil, false, errors.Wrap(err, "DecodeIndex")
+		return nil, errors.Wrap(err, "DecodeIndex")
 	}
 
 	idx = NewIndex()
@@ -537,38 +516,6 @@ func DecodeIndex(buf []byte, id restic.ID) (idx *Index, oldFormat bool, err erro
 	idx.ids = append(idx.ids, id)
 	idx.final = true
 
-	debug.Log("done")
-	return idx, false, nil
-}
-
-// DecodeOldIndex loads and unserializes an index in the old format from rd.
-func decodeOldIndex(buf []byte) (idx *Index, err error) {
-	debug.Log("Start decoding old index")
-	list := []*packJSON{}
-
-	err = json.Unmarshal(buf, &list)
-	if err != nil {
-		debug.Log("Error %#v", err)
-		return nil, errors.Wrap(err, "Decode")
-	}
-
-	idx = NewIndex()
-	for _, pack := range list {
-		packID := idx.addToPacks(pack.ID)
-
-		for _, blob := range pack.Blobs {
-			idx.store(packID, restic.Blob{
-				BlobHandle: restic.BlobHandle{
-					Type: blob.Type,
-					ID:   blob.ID},
-				Offset: blob.Offset,
-				Length: blob.Length,
-				// no compressed length in the old index format
-			})
-		}
-	}
-	idx.final = true
-
 	debug.Log("done")
 	return idx, nil
 }
diff --git a/internal/repository/index/index_parallel.go b/internal/repository/index/index_parallel.go
index 3d5621a2d..fda5123d3 100644
--- a/internal/repository/index/index_parallel.go
+++ b/internal/repository/index/index_parallel.go
@@ -12,7 +12,7 @@ import (
 // It is guaranteed that the function is not run concurrently. If the callback
 // returns an error, this function is cancelled and also returns that error.
 func ForAllIndexes(ctx context.Context, lister restic.Lister, repo restic.LoaderUnpacked,
-	fn func(id restic.ID, index *Index, oldFormat bool, err error) error) error {
+	fn func(id restic.ID, index *Index, err error) error) error {
 
 	// decoding an index can take quite some time such that this can be both CPU- or IO-bound
 	// as the whole index is kept in memory anyways, a few workers too much don't matter
@@ -22,15 +22,14 @@ func ForAllIndexes(ctx context.Context, lister restic.Lister, repo restic.Loader
 	return restic.ParallelList(ctx, lister, restic.IndexFile, workerCount, func(ctx context.Context, id restic.ID, _ int64) error {
 		var err error
 		var idx *Index
-		oldFormat := false
 
 		buf, err := repo.LoadUnpacked(ctx, restic.IndexFile, id)
 		if err == nil {
-			idx, oldFormat, err = DecodeIndex(buf, id)
+			idx, err = DecodeIndex(buf, id)
 		}
 
 		m.Lock()
 		defer m.Unlock()
-		return fn(id, idx, oldFormat, err)
+		return fn(id, idx, err)
 	})
 }
diff --git a/internal/repository/index/index_parallel_test.go b/internal/repository/index/index_parallel_test.go
index 38dafb507..96f1c2a6a 100644
--- a/internal/repository/index/index_parallel_test.go
+++ b/internal/repository/index/index_parallel_test.go
@@ -27,7 +27,7 @@ func TestRepositoryForAllIndexes(t *testing.T) {
 	// check that all expected indexes are loaded without errors
 	indexIDs := restic.NewIDSet()
 	var indexErr error
-	rtest.OK(t, index.ForAllIndexes(context.TODO(), repo, repo, func(id restic.ID, index *index.Index, oldFormat bool, err error) error {
+	rtest.OK(t, index.ForAllIndexes(context.TODO(), repo, repo, func(id restic.ID, index *index.Index, err error) error {
 		if err != nil {
 			indexErr = err
 		}
@@ -40,7 +40,7 @@ func TestRepositoryForAllIndexes(t *testing.T) {
 	// must failed with the returned error
 	iterErr := errors.New("error to pass upwards")
 
-	err := index.ForAllIndexes(context.TODO(), repo, repo, func(id restic.ID, index *index.Index, oldFormat bool, err error) error {
+	err := index.ForAllIndexes(context.TODO(), repo, repo, func(id restic.ID, index *index.Index, err error) error {
 		return iterErr
 	})
 
diff --git a/internal/repository/index/index_test.go b/internal/repository/index/index_test.go
index bf752d3d3..93803603d 100644
--- a/internal/repository/index/index_test.go
+++ b/internal/repository/index/index_test.go
@@ -8,7 +8,6 @@ import (
 	"sync"
 	"testing"
 
-	"github.com/restic/restic/internal/feature"
 	"github.com/restic/restic/internal/repository/index"
 	"github.com/restic/restic/internal/restic"
 	rtest "github.com/restic/restic/internal/test"
@@ -53,11 +52,9 @@ func TestIndexSerialize(t *testing.T) {
 	rtest.OK(t, err)
 
 	idx2ID := restic.NewRandomID()
-	idx2, oldFormat, err := index.DecodeIndex(wr.Bytes(), idx2ID)
+	idx2, err := index.DecodeIndex(wr.Bytes(), idx2ID)
 	rtest.OK(t, err)
-	rtest.Assert(t, idx2 != nil,
-		"nil returned for decoded index")
-	rtest.Assert(t, !oldFormat, "new index format recognized as old format")
+	rtest.Assert(t, idx2 != nil, "nil returned for decoded index")
 	indexID, err := idx2.IDs()
 	rtest.OK(t, err)
 	rtest.Equals(t, indexID, restic.IDs{idx2ID})
@@ -123,13 +120,10 @@ func TestIndexSerialize(t *testing.T) {
 	rtest.OK(t, err)
 	rtest.Equals(t, restic.IDs{id}, ids)
 
-	idx3, oldFormat, err := index.DecodeIndex(wr3.Bytes(), id)
+	idx3, err := index.DecodeIndex(wr3.Bytes(), id)
 	rtest.OK(t, err)
-	rtest.Assert(t, idx3 != nil,
-		"nil returned for decoded index")
-	rtest.Assert(t, idx3.Final(),
-		"decoded index is not final")
-	rtest.Assert(t, !oldFormat, "new index format recognized as old format")
+	rtest.Assert(t, idx3 != nil, "nil returned for decoded index")
+	rtest.Assert(t, idx3.Final(), "decoded index is not final")
 
 	// all new blobs must be in the index
 	for _, testBlob := range newtests {
@@ -246,31 +240,6 @@ var docExampleV2 = []byte(`
   }
 `)
 
-var docOldExample = []byte(`
-[ {
-  "id": "73d04e6125cf3c28a299cc2f3cca3b78ceac396e4fcf9575e34536b26782413c",
-  "blobs": [
-	{
-	  "id": "3ec79977ef0cf5de7b08cd12b874cd0f62bbaf7f07f3497a5b1bbcc8cb39b1ce",
-	  "type": "data",
-	  "offset": 0,
-	  "length": 38
-	},{
-	  "id": "9ccb846e60d90d4eb915848add7aa7ea1e4bbabfc60e573db9f7bfb2789afbae",
-	  "type": "tree",
-	  "offset": 38,
-	  "length": 112
-	},
-	{
-	  "id": "d3dc577b4ffd38cc4b32122cabf8655a0223ed22edfd93b353dc0c3f2b0fdf66",
-	  "type": "data",
-	  "offset": 150,
-	  "length": 123
-	}
-  ]
-} ]
-`)
-
 var exampleTests = []struct {
 	id, packID         restic.ID
 	tpe                restic.BlobType
@@ -312,9 +281,8 @@ func TestIndexUnserialize(t *testing.T) {
 		{docExampleV1, 1},
 		{docExampleV2, 2},
 	} {
-		idx, oldFormat, err := index.DecodeIndex(task.idxBytes, restic.NewRandomID())
+		idx, err := index.DecodeIndex(task.idxBytes, restic.NewRandomID())
 		rtest.OK(t, err)
-		rtest.Assert(t, !oldFormat, "new index format recognized as old format")
 
 		for _, test := range exampleTests {
 			list := idx.Lookup(restic.BlobHandle{ID: test.id, Type: test.tpe}, nil)
@@ -387,7 +355,7 @@ func BenchmarkDecodeIndex(b *testing.B) {
 	b.ResetTimer()
 
 	for i := 0; i < b.N; i++ {
-		_, _, err := index.DecodeIndex(benchmarkIndexJSON, id)
+		_, err := index.DecodeIndex(benchmarkIndexJSON, id)
 		rtest.OK(b, err)
 	}
 }
@@ -400,7 +368,7 @@ func BenchmarkDecodeIndexParallel(b *testing.B) {
 
 	b.RunParallel(func(pb *testing.PB) {
 		for pb.Next() {
-			_, _, err := index.DecodeIndex(benchmarkIndexJSON, id)
+			_, err := index.DecodeIndex(benchmarkIndexJSON, id)
 			rtest.OK(b, err)
 		}
 	})
@@ -426,27 +394,6 @@ func BenchmarkEncodeIndex(b *testing.B) {
 	}
 }
 
-func TestIndexUnserializeOld(t *testing.T) {
-	defer feature.TestSetFlag(t, feature.Flag, feature.DeprecateLegacyIndex, false)()
-
-	idx, oldFormat, err := index.DecodeIndex(docOldExample, restic.NewRandomID())
-	rtest.OK(t, err)
-	rtest.Assert(t, oldFormat, "old index format recognized as new format")
-
-	for _, test := range exampleTests {
-		list := idx.Lookup(restic.BlobHandle{ID: test.id, Type: test.tpe}, nil)
-		if len(list) != 1 {
-			t.Errorf("expected one result for blob %v, got %v: %v", test.id.Str(), len(list), list)
-		}
-		blob := list[0]
-
-		rtest.Equals(t, test.packID, blob.PackID)
-		rtest.Equals(t, test.tpe, blob.Type)
-		rtest.Equals(t, test.offset, blob.Offset)
-		rtest.Equals(t, test.length, blob.Length)
-	}
-}
-
 func TestIndexPacks(t *testing.T) {
 	idx := index.NewIndex()
 	packs := restic.NewIDSet()
diff --git a/internal/repository/index/master_index.go b/internal/repository/index/master_index.go
index 9b5c4f9f8..2600fe350 100644
--- a/internal/repository/index/master_index.go
+++ b/internal/repository/index/master_index.go
@@ -265,7 +265,7 @@ func (mi *MasterIndex) MergeFinalIndexes() error {
 	return nil
 }
 
-func (mi *MasterIndex) Load(ctx context.Context, r restic.ListerLoaderUnpacked, p *progress.Counter, cb func(id restic.ID, idx *Index, oldFormat bool, err error) error) error {
+func (mi *MasterIndex) Load(ctx context.Context, r restic.ListerLoaderUnpacked, p *progress.Counter, cb func(id restic.ID, idx *Index, err error) error) error {
 	indexList, err := restic.MemorizeList(ctx, r, restic.IndexFile)
 	if err != nil {
 		return err
@@ -284,12 +284,12 @@ func (mi *MasterIndex) Load(ctx context.Context, r restic.ListerLoaderUnpacked,
 		defer p.Done()
 	}
 
-	err = ForAllIndexes(ctx, indexList, r, func(id restic.ID, idx *Index, oldFormat bool, err error) error {
+	err = ForAllIndexes(ctx, indexList, r, func(id restic.ID, idx *Index, err error) error {
 		if p != nil {
 			p.Add(1)
 		}
 		if cb != nil {
-			err = cb(id, idx, oldFormat, err)
+			err = cb(id, idx, err)
 		}
 		if err != nil {
 			return err
@@ -365,8 +365,7 @@ func (mi *MasterIndex) Rewrite(ctx context.Context, repo restic.Unpacked, exclud
 
 	var rewriteWg sync.WaitGroup
 	type rewriteTask struct {
-		idx       *Index
-		oldFormat bool
+		idx *Index
 	}
 	rewriteCh := make(chan rewriteTask)
 	loader := func() error {
@@ -376,13 +375,13 @@ func (mi *MasterIndex) Rewrite(ctx context.Context, repo restic.Unpacked, exclud
 			if err != nil {
 				return fmt.Errorf("LoadUnpacked(%v): %w", id.Str(), err)
 			}
-			idx, oldFormat, err := DecodeIndex(buf, id)
+			idx, err := DecodeIndex(buf, id)
 			if err != nil {
 				return err
 			}
 
 			select {
-			case rewriteCh <- rewriteTask{idx, oldFormat}:
+			case rewriteCh <- rewriteTask{idx}:
 			case <-wgCtx.Done():
 				return wgCtx.Err()
 			}
@@ -411,8 +410,8 @@ func (mi *MasterIndex) Rewrite(ctx context.Context, repo restic.Unpacked, exclud
 		defer close(saveCh)
 		newIndex := NewIndex()
 		for task := range rewriteCh {
-			// always rewrite indexes using the old format, that include a pack that must be removed or that are not full
-			if !task.oldFormat && len(task.idx.Packs().Intersect(excludePacks)) == 0 && IndexFull(task.idx) {
+			// always rewrite indexes that include a pack that must be removed or that are not full
+			if len(task.idx.Packs().Intersect(excludePacks)) == 0 && IndexFull(task.idx) {
 				// make sure that each pack is only stored exactly once in the index
 				excludePacks.Merge(task.idx.Packs())
 				// index is already up to date
diff --git a/internal/repository/repair_index.go b/internal/repository/repair_index.go
index 770809254..bff7ec5da 100644
--- a/internal/repository/repair_index.go
+++ b/internal/repository/repair_index.go
@@ -33,7 +33,7 @@ func RepairIndex(ctx context.Context, repo *Repository, opts RepairIndexOptions,
 	} else {
 		printer.P("loading indexes...\n")
 		mi := index.NewMasterIndex()
-		err := index.ForAllIndexes(ctx, repo, repo, func(id restic.ID, idx *index.Index, _ bool, err error) error {
+		err := index.ForAllIndexes(ctx, repo, repo, func(id restic.ID, idx *index.Index, err error) error {
 			if err != nil {
 				printer.E("removing invalid index %v: %v\n", id, err)
 				obsoleteIndexes = append(obsoleteIndexes, id)
diff --git a/internal/repository/repository_test.go b/internal/repository/repository_test.go
index ea21ea3f3..3467a9cfa 100644
--- a/internal/repository/repository_test.go
+++ b/internal/repository/repository_test.go
@@ -4,10 +4,8 @@ import (
 	"bytes"
 	"context"
 	"crypto/sha256"
-	"fmt"
 	"io"
 	"math/rand"
-	"os"
 	"path/filepath"
 	"strings"
 	"sync"
@@ -261,11 +259,7 @@ func loadIndex(ctx context.Context, repo restic.LoaderUnpacked, id restic.ID) (*
 		return nil, err
 	}
 
-	idx, oldFormat, err := index.DecodeIndex(buf, id)
-	if oldFormat {
-		fmt.Fprintf(os.Stderr, "index %v has old format\n", id.Str())
-	}
-	return idx, err
+	return index.DecodeIndex(buf, id)
 }
 
 func TestRepositoryLoadUnpackedBroken(t *testing.T) {