diff --git a/dagsync/subscriber.go b/dagsync/subscriber.go
index e742859..a98638f 100644
--- a/dagsync/subscriber.go
+++ b/dagsync/subscriber.go
@@ -98,6 +98,12 @@ type Subscriber struct {
 	segDepthLimit int64
 
 	receiver *announce.Receiver
+
+	// Track explicit Sync calls in progress and allow them to complete before
+	// closing subscriber.
+	expSyncClosed bool
+	expSyncMutex  sync.Mutex
+	expSyncWG     sync.WaitGroup
 }
 
 // SyncFinished notifies an OnSyncFinished reader that a specified peer
@@ -290,6 +296,13 @@ func (s *Subscriber) doClose() error {
 	// Cancel idle handler cleaner.
 	close(s.closing)
 
+	// Block any additional explicit Sync calls.
+	s.expSyncMutex.Lock()
+	s.expSyncClosed = true
+	s.expSyncMutex.Unlock()
+	// Wait for explicit Syncs calls to finish.
+	s.expSyncWG.Wait()
+
 	// Close receiver and wait for watch to exit.
 	err := s.receiver.Close()
 	if err != nil {
@@ -403,6 +416,15 @@ func (s *Subscriber) RemoveHandler(peerID peer.ID) bool {
 //
 // See: ExploreRecursiveWithStopNode.
 func (s *Subscriber) Sync(ctx context.Context, peerInfo peer.AddrInfo, nextCid cid.Cid, sel ipld.Node, options ...SyncOption) (cid.Cid, error) {
+	s.expSyncMutex.Lock()
+	if s.expSyncClosed {
+		s.expSyncMutex.Unlock()
+		return cid.Undef, errors.New("shutdown")
+	}
+	s.expSyncWG.Add(1)
+	s.expSyncMutex.Unlock()
+	defer s.expSyncWG.Done()
+
 	defaultOptions := []SyncOption{
 		ScopedBlockHook(s.generalBlockHook),
 		ScopedSegmentDepthLimit(s.segDepthLimit)}
diff --git a/go.mod b/go.mod
index 9d7d8b6..c31f656 100644
--- a/go.mod
+++ b/go.mod
@@ -11,7 +11,7 @@ require (
 	github.com/ipfs/go-ipld-format v0.3.0
 	github.com/ipfs/go-log/v2 v2.5.1
 	github.com/ipld/go-ipld-prime v0.20.0
-	github.com/libp2p/go-libp2p v0.27.4
+	github.com/libp2p/go-libp2p v0.27.5
 	github.com/libp2p/go-libp2p-gostream v0.6.0
 	github.com/libp2p/go-libp2p-pubsub v0.9.3
 	github.com/libp2p/go-msgio v0.3.0
@@ -22,7 +22,7 @@ require (
 	github.com/multiformats/go-multistream v0.4.1
 	github.com/multiformats/go-varint v0.0.7
 	github.com/stretchr/testify v1.8.2
-	github.com/whyrusleeping/cbor-gen v0.0.0-20230126041949-52956bd4c9aa
+	github.com/whyrusleeping/cbor-gen v0.0.0-20230418232409-daab9ece03a0
 	golang.org/x/crypto v0.7.0
 	golang.org/x/xerrors v0.0.0-20220907171357-04be3eba64a2
 	google.golang.org/protobuf v1.30.0
diff --git a/go.sum b/go.sum
index c5bb064..e61e018 100644
--- a/go.sum
+++ b/go.sum
@@ -324,8 +324,8 @@ github.com/libp2p/go-cidranger v1.1.0 h1:ewPN8EZ0dd1LSnrtuwd4709PXVcITVeuwbag38y
 github.com/libp2p/go-cidranger v1.1.0/go.mod h1:KWZTfSr+r9qEo9OkI9/SIEeAtw+NNoU0dXIXt15Okic=
 github.com/libp2p/go-flow-metrics v0.1.0 h1:0iPhMI8PskQwzh57jB9WxIuIOQ0r+15PChFGkx3Q3WM=
 github.com/libp2p/go-flow-metrics v0.1.0/go.mod h1:4Xi8MX8wj5aWNDAZttg6UPmc0ZrnFNsMtpsYUClFtro=
-github.com/libp2p/go-libp2p v0.27.4 h1:zliwN9xuzCBqCtWe0XjLKJGK6EIZTkp9L1e15wBpiOU=
-github.com/libp2p/go-libp2p v0.27.4/go.mod h1:oMfQGTb9CHnrOuSM6yMmyK2lXz3qIhnkn2+oK3B1Y2g=
+github.com/libp2p/go-libp2p v0.27.5 h1:KwA7pXKXpz8hG6Cr1fMA7UkgleogcwQj0sxl5qquWRg=
+github.com/libp2p/go-libp2p v0.27.5/go.mod h1:oMfQGTb9CHnrOuSM6yMmyK2lXz3qIhnkn2+oK3B1Y2g=
 github.com/libp2p/go-libp2p-asn-util v0.3.0 h1:gMDcMyYiZKkocGXDQ5nsUQyquC9+H+iLEQHwOCZ7s8s=
 github.com/libp2p/go-libp2p-asn-util v0.3.0/go.mod h1:B1mcOrKUE35Xq/ASTmQ4tN3LNzVVaMNmq2NACuqyB9w=
 github.com/libp2p/go-libp2p-gostream v0.6.0 h1:QfAiWeQRce6pqnYfmIVWJFXNdDyfiR/qkCnjyaZUPYU=
@@ -542,8 +542,8 @@ github.com/whyrusleeping/cbor-gen v0.0.0-20191216205031-b047b6acb3c0/go.mod h1:x
 github.com/whyrusleeping/cbor-gen v0.0.0-20200123233031-1cdf64d27158/go.mod h1:Xj/M2wWU+QdTdRbu/L/1dIZY8/Wb2K9pAhtroQuxJJI=
 github.com/whyrusleeping/cbor-gen v0.0.0-20200710004633-5379fc63235d/go.mod h1:fgkXqYy7bV2cFeIEOkVTZS/WjXARfBqSH6Q2qHL33hQ=
 github.com/whyrusleeping/cbor-gen v0.0.0-20200826160007-0b9f6c5fb163/go.mod h1:fgkXqYy7bV2cFeIEOkVTZS/WjXARfBqSH6Q2qHL33hQ=
-github.com/whyrusleeping/cbor-gen v0.0.0-20230126041949-52956bd4c9aa h1:EyA027ZAkuaCLoxVX4r1TZMPy1d31fM6hbfQ4OU4I5o=
-github.com/whyrusleeping/cbor-gen v0.0.0-20230126041949-52956bd4c9aa/go.mod h1:fgkXqYy7bV2cFeIEOkVTZS/WjXARfBqSH6Q2qHL33hQ=
+github.com/whyrusleeping/cbor-gen v0.0.0-20230418232409-daab9ece03a0 h1:XYEgH2nJgsrcrj32p+SAbx6T3s/6QknOXezXtz7kzbg=
+github.com/whyrusleeping/cbor-gen v0.0.0-20230418232409-daab9ece03a0/go.mod h1:fgkXqYy7bV2cFeIEOkVTZS/WjXARfBqSH6Q2qHL33hQ=
 github.com/whyrusleeping/chunker v0.0.0-20181014151217-fe64bd25879f h1:jQa4QT2UP9WYv2nzyawpKMOCl+Z/jW7djv2/J50lj9E=
 github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=