diff --git a/dagstore.go b/dagstore.go
index d615b26..bb53477 100644
--- a/dagstore.go
+++ b/dagstore.go
@@ -9,6 +9,7 @@ import (
 
 	mh "github.com/multiformats/go-multihash"
 
+	"github.com/ipld/go-car/v2"
 	carindex "github.com/ipld/go-car/v2/index"
 
 	ds "github.com/ipfs/go-datastore"
@@ -73,6 +74,7 @@ type DAGStore struct {
 	config  Config
 	indices index.FullIndexRepo
 	store   ds.Datastore
+	indexer ShardIndexer
 
 	// TopLevelIndex is the top level (cid -> []shards) index that maps a cid to all the shards that is present in.
 	TopLevelIndex index.Inverted
@@ -138,6 +140,8 @@ type ShardResult struct {
 	Accessor *ShardAccessor
 }
 
+type ShardIndexer func(context.Context, shard.Key, mount.Reader) (carindex.Index, error)
+
 type Config struct {
 	// TransientsDir is the path to directory where local transient files will
 	// be created for remote mounts.
@@ -183,6 +187,10 @@ type Config struct {
 	// RecoverOnStart specifies whether failed shards should be recovered
 	// on start.
 	RecoverOnStart RecoverOnStartPolicy
+
+	// ShardIndexer sets a custom callback for determining the index
+	// mapping of CID->Offset that should be registered for a shard.
+	ShardIndexer ShardIndexer
 }
 
 // NewDAGStore constructs a new DAG store with the supplied configuration.
@@ -207,6 +215,12 @@ func NewDAGStore(cfg Config) (*DAGStore, error) {
 		log.Info("using in-memory inverted index")
 		cfg.TopLevelIndex = index.NewInverted(dssync.MutexWrap(ds.NewMapDatastore()))
 	}
+	// default indexer
+	if cfg.ShardIndexer == nil {
+		cfg.ShardIndexer = func(_ context.Context, _ shard.Key, r mount.Reader) (carindex.Index, error) {
+			return car.ReadOrGenerateIndex(r, car.ZeroLengthSectionAsEOF(true), car.StoreIdentityCIDs(true))
+		}
+	}
 
 	// handle the datastore.
 	if cfg.Datastore == nil {
@@ -229,6 +243,7 @@ func NewDAGStore(cfg Config) (*DAGStore, error) {
 		TopLevelIndex:       cfg.TopLevelIndex,
 		shards:              make(map[shard.Key]*Shard),
 		store:               cfg.Datastore,
+		indexer:             cfg.ShardIndexer,
 		externalCh:          make(chan *task, 128),     // len=128, concurrent external tasks that can be queued up before exercising backpressure.
 		internalCh:          make(chan *task, 1),       // len=1, because eventloop will only ever stage another internal event.
 		completionCh:        make(chan *task, 64),      // len=64, hitting this limit will just make async tasks wait.
@@ -460,7 +475,8 @@ type RecoverOpts struct {
 // will be notified when it completes.
 //
 // TODO add an operation identifier to ShardResult -- starts to look like
-//  a Trace event?
+//
+//	a Trace event?
 func (d *DAGStore) RecoverShard(ctx context.Context, key shard.Key, out chan ShardResult, _ RecoverOpts) error {
 	d.lk.Lock()
 	s, ok := d.shards[key]
diff --git a/dagstore_async.go b/dagstore_async.go
index 13f5a0c..d85fe18 100644
--- a/dagstore_async.go
+++ b/dagstore_async.go
@@ -5,7 +5,6 @@ import (
 
 	"github.com/filecoin-project/dagstore/index"
 
-	"github.com/ipld/go-car/v2"
 	carindex "github.com/ipld/go-car/v2/index"
 	"github.com/multiformats/go-multihash"
 
@@ -120,7 +119,7 @@ func (d *DAGStore) initializeShard(ctx context.Context, s *Shard, mnt mount.Moun
 	var idx carindex.Index
 	err = d.throttleIndex.Do(ctx, func(_ context.Context) error {
 		var err error
-		idx, err = car.ReadOrGenerateIndex(reader, car.ZeroLengthSectionAsEOF(true), car.StoreIdentityCIDs(true))
+		idx, err = d.indexer(ctx, s.key, reader)
 		if err == nil {
 			log.Debugw("initialize: finished generating index for shard", "shard", s.key)
 		} else {