diff --git a/changelog/unreleased/issue-4602 b/changelog/unreleased/issue-4602
new file mode 100644
index 000000000..3cba63876
--- /dev/null
+++ b/changelog/unreleased/issue-4602
@@ -0,0 +1,13 @@
+Change: Deprecate legacy index format
+
+Support for the legacy index format used by restic before version 0.2.0 has
+been depreacted and will be removed in the next minor restic version. You can
+use `restic repair index` to update the index to the current format.
+
+It is possible to temporarily reenable support for the legacy index format by
+setting the environment variable
+`RESTIC_FEATURES=deprecate-legacy-index=false`. Note that this feature flag
+will be removed in the next minor restic version.
+
+https://github.com/restic/restic/issues/4602
+https://github.com/restic/restic/pull/4724
diff --git a/cmd/restic/cmd_check.go b/cmd/restic/cmd_check.go
index 990702b61..cbe388877 100644
--- a/cmd/restic/cmd_check.go
+++ b/cmd/restic/cmd_check.go
@@ -231,12 +231,17 @@ 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, *checker.ErrOldIndexFormat:
+		case *checker.ErrDuplicatePacks:
 			Printf("%v\n", hint)
 			suggestIndexRebuild = true
+		case *checker.ErrOldIndexFormat:
+			Warnf("error: %v\n", hint)
+			suggestLegacyIndexRebuild = true
+			errorsFound = true
 		case *checker.ErrMixedPack:
 			Printf("%v\n", hint)
 			mixedFound = true
@@ -247,7 +252,10 @@ func runCheck(ctx context.Context, opts CheckOptions, gopts GlobalOptions, args
 	}
 
 	if suggestIndexRebuild {
-		Printf("Duplicate packs/old indexes are non-critical, you can run `restic repair index' to correct this.\n")
+		Printf("Duplicate packs are non-critical, you can run `restic repair index' to correct this.\n")
+	}
+	if suggestLegacyIndexRebuild {
+		Warnf("Found indexes using the legacy format, you must run `restic repair index' to correct this.\n")
 	}
 	if mixedFound {
 		Printf("Mixed packs with tree and data blobs are non-critical, you can run `restic prune` to correct this.\n")
diff --git a/cmd/restic/testdata/repo-restore-permissions-test.tar.gz b/cmd/restic/testdata/repo-restore-permissions-test.tar.gz
index 36aa62dbf..dc8e9bc80 100644
Binary files a/cmd/restic/testdata/repo-restore-permissions-test.tar.gz and b/cmd/restic/testdata/repo-restore-permissions-test.tar.gz differ
diff --git a/internal/feature/registry.go b/internal/feature/registry.go
index 7a9cbf560..620c9ec35 100644
--- a/internal/feature/registry.go
+++ b/internal/feature/registry.go
@@ -5,11 +5,13 @@ var Flag = New()
 
 // flag names are written in kebab-case
 const (
-	ExampleFeature FlagName = "example-feature"
+	ExampleFeature       FlagName = "example-feature"
+	DeprecateLegacyIndex FlagName = "deprecate-legacy-index"
 )
 
 func init() {
 	Flag.SetFlags(map[FlagName]FlagDesc{
-		ExampleFeature: {Type: Alpha, Description: "just for testing"},
+		ExampleFeature:       {Type: Alpha, Description: "just for testing"},
+		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."},
 	})
 }
diff --git a/internal/index/index.go b/internal/index/index.go
index ecd481594..1fb2c155e 100644
--- a/internal/index/index.go
+++ b/internal/index/index.go
@@ -3,12 +3,14 @@ package index
 import (
 	"context"
 	"encoding/json"
+	"fmt"
 	"io"
 	"sync"
 	"time"
 
 	"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"
@@ -515,8 +517,13 @@ func DecodeIndex(buf []byte, id restic.ID) (idx *Index, oldFormat bool, err erro
 		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
 		}
 
diff --git a/internal/index/index_test.go b/internal/index/index_test.go
index 4f0dbd2a0..78e4800ca 100644
--- a/internal/index/index_test.go
+++ b/internal/index/index_test.go
@@ -8,6 +8,7 @@ import (
 	"sync"
 	"testing"
 
+	"github.com/restic/restic/internal/feature"
 	"github.com/restic/restic/internal/index"
 	"github.com/restic/restic/internal/restic"
 	rtest "github.com/restic/restic/internal/test"
@@ -427,6 +428,8 @@ 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")