diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5cb7b7d433..b8fe89bdc6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,8 @@
 
 ## HEAD
 
+* Update ctclient tool to support SCT extensions field by @liweitianux in https://github.com/google/certificate-transparency-go/pull/1645
+
 ## v1.3.1
 
 * Add AllLogListSignatureURL by @AlexLaroche in https://github.com/google/certificate-transparency-go/pull/1634
diff --git a/client/ctclient/cmd/get_entries.go b/client/ctclient/cmd/get_entries.go
index 33e583473b..69b2c4942b 100644
--- a/client/ctclient/cmd/get_entries.go
+++ b/client/ctclient/cmd/get_entries.go
@@ -80,6 +80,9 @@ func showRawLogEntry(rle *ct.RawLogEntry) {
 	ts := rle.Leaf.TimestampedEntry
 	when := ct.TimestampToTime(ts.Timestamp)
 	fmt.Printf("Index=%d Timestamp=%d (%v) ", rle.Index, ts.Timestamp, when)
+	if len(ts.Extensions) > 0 {
+		fmt.Printf("Extensions=%x ", ts.Extensions)
+	}
 
 	switch ts.EntryType {
 	case ct.X509LogEntryType:
diff --git a/client/ctclient/cmd/get_inclusion_proof.go b/client/ctclient/cmd/get_inclusion_proof.go
index 1d2881e6bc..03ca2d3a30 100644
--- a/client/ctclient/cmd/get_inclusion_proof.go
+++ b/client/ctclient/cmd/get_inclusion_proof.go
@@ -17,6 +17,7 @@ package cmd
 import (
 	"context"
 	"crypto/sha256"
+	"encoding/hex"
 	"encoding/pem"
 	"fmt"
 	"os"
@@ -35,15 +36,16 @@ import (
 )
 
 var (
-	leafHash  string
-	certChain string
-	timestamp int64
-	treeSize  uint64
+	leafHash   string
+	certChain  string
+	timestamp  int64
+	treeSize   uint64
+	extensions string
 )
 
 func init() {
 	cmd := cobra.Command{
-		Use:     fmt.Sprintf("get-inclusion-proof %s {--leaf_hash=hash | --cert_chain=file} [--timestamp=ts] [--size=N]", connectionFlags),
+		Use:     fmt.Sprintf("get-inclusion-proof %s {--leaf_hash=hash | --cert_chain=file} [--timestamp=ts] [--size=N] [--extensions=exts]", connectionFlags),
 		Aliases: []string{"getinclusionproof", "inclusion-proof", "inclusion"},
 		Short:   "Fetch and verify the inclusion proof for an entry",
 		Args:    cobra.MaximumNArgs(0),
@@ -54,6 +56,7 @@ func init() {
 	cmd.Flags().StringVar(&leafHash, "leaf_hash", "", "Leaf hash to retrieve (as hex string or base64)")
 	cmd.Flags().StringVar(&certChain, "cert_chain", "", "Name of file containing certificate chain as concatenated PEM files")
 	cmd.Flags().Int64Var(&timestamp, "timestamp", 0, "Timestamp to use for inclusion checking")
+	cmd.Flags().StringVar(&extensions, "extensions", "", "CT extensions in SCT (as hex string)")
 	cmd.Flags().Uint64Var(&treeSize, "size", 0, "Tree size to query at")
 	rootCmd.AddCommand(&cmd)
 }
@@ -61,6 +64,14 @@ func init() {
 // runGetInclusionProof runs the get-inclusion-proof command.
 func runGetInclusionProof(ctx context.Context) {
 	logClient := connect(ctx)
+	var ctexts ct.CTExtensions
+	if len(extensions) > 0 {
+		exts, err := hex.DecodeString(extensions)
+		if err != nil {
+			klog.Exitf("Invalid --extensions supplied: %v", err)
+		}
+		ctexts = ct.CTExtensions(exts)
+	}
 	var hash []byte
 	if len(leafHash) > 0 {
 		var err error
@@ -70,13 +81,16 @@ func runGetInclusionProof(ctx context.Context) {
 		}
 	} else if len(certChain) > 0 {
 		// Build a leaf hash from the chain and a timestamp.
-		chain, entryTimestamp := chainFromFile(certChain)
+		chain, entryTimestamp, entryCTExts := chainFromFile(certChain)
 		if timestamp != 0 {
 			entryTimestamp = timestamp // Use user-specified timestamp.
 		}
 		if entryTimestamp == 0 {
 			klog.Exit("No timestamp available to accompany certificate")
 		}
+		if len(entryCTExts) == 0 {
+			entryCTExts = ctexts
+		}
 
 		var leafEntry *ct.MerkleTreeLeaf
 		cert, err := x509.ParseCertificate(chain[0].Data)
@@ -92,6 +106,7 @@ func runGetInclusionProof(ctx context.Context) {
 			leafEntry = ct.CreateX509MerkleTreeLeaf(chain[0], uint64(entryTimestamp))
 		}
 
+		leafEntry.TimestampedEntry.Extensions = entryCTExts
 		leafHash, err := ct.LeafHashForLeaf(leafEntry)
 		if err != nil {
 			klog.Exitf("Failed to create hash of leaf: %v", err)
@@ -139,7 +154,7 @@ func getInclusionProofForHash(ctx context.Context, logClient client.CheckLogClie
 	}
 }
 
-func chainFromFile(filename string) ([]ct.ASN1Cert, int64) {
+func chainFromFile(filename string) ([]ct.ASN1Cert, int64, []byte) {
 	contents, err := os.ReadFile(filename)
 	if err != nil {
 		klog.Exitf("Failed to read certificate file: %v", err)
@@ -160,9 +175,12 @@ func chainFromFile(filename string) ([]ct.ASN1Cert, int64) {
 		klog.Exitf("No certificates found in %s", certChain)
 	}
 
-	// Also look for something like a text timestamp for convenience.
+	// Also look for something like a text timestamp and a hex extensions
+	// for convenience.
 	var timestamp int64
+	var extensions []byte
 	tsRE := regexp.MustCompile(`Timestamp[:=](\d+)`)
+	extsRE := regexp.MustCompile(`Extensions[:=]([a-fA-F0-9]+)`)
 	for _, line := range strings.Split(string(contents), "\n") {
 		x := tsRE.FindStringSubmatch(line)
 		if len(x) > 1 {
@@ -171,6 +189,13 @@ func chainFromFile(filename string) ([]ct.ASN1Cert, int64) {
 				break
 			}
 		}
+		x = extsRE.FindStringSubmatch(line)
+		if len(x) > 1 {
+			extensions, err = hex.DecodeString(x[1])
+			if err != nil {
+				break
+			}
+		}
 	}
-	return chain, timestamp
+	return chain, timestamp, extensions
 }
diff --git a/client/ctclient/cmd/upload.go b/client/ctclient/cmd/upload.go
index 95adda9145..743d61863a 100644
--- a/client/ctclient/cmd/upload.go
+++ b/client/ctclient/cmd/upload.go
@@ -50,7 +50,7 @@ func runUpload(ctx context.Context) {
 	if certChain == "" {
 		klog.Exitf("No certificate chain file specified with -cert_chain")
 	}
-	chain, _ := chainFromFile(certChain)
+	chain, _, _ := chainFromFile(certChain)
 
 	// Examine the leaf to see if it looks like a pre-certificate.
 	isPrecert := false
@@ -74,6 +74,7 @@ func runUpload(ctx context.Context) {
 	}
 	// Calculate the leaf hash.
 	leafEntry := ct.CreateX509MerkleTreeLeaf(chain[0], sct.Timestamp)
+	leafEntry.TimestampedEntry.Extensions = sct.Extensions
 	leafHash, err := ct.LeafHashForLeaf(leafEntry)
 	if err != nil {
 		klog.Exitf("Failed to create hash of leaf: %v", err)
@@ -84,6 +85,11 @@ func runUpload(ctx context.Context) {
 	fmt.Printf("Uploaded chain of %d certs to %v log at %v, timestamp: %d (%v)\n", len(chain), sct.SCTVersion, logClient.BaseURI(), sct.Timestamp, when)
 	fmt.Printf("LogID: %x\n", sct.LogID.KeyID[:])
 	fmt.Printf("LeafHash: %x\n", leafHash)
+	if len(sct.Extensions) > 0 {
+		fmt.Printf("Extensions: %x\n", sct.Extensions)
+	} else {
+		fmt.Printf("Extensions: (nil)\n")
+	}
 	fmt.Printf("Signature: %v\n", signatureToString(&sct.Signature))
 
 	age := time.Since(when)
diff --git a/client/logclient.go b/client/logclient.go
index 7842c8e288..0e90c1077f 100644
--- a/client/logclient.go
+++ b/client/logclient.go
@@ -160,6 +160,7 @@ func (c *LogClient) VerifySCTSignature(sct ct.SignedCertificateTimestamp, ctype
 	if err != nil {
 		return fmt.Errorf("failed to build MerkleTreeLeaf: %v", err)
 	}
+	leaf.TimestampedEntry.Extensions = sct.Extensions
 	entry := ct.LogEntry{Leaf: *leaf}
 	return c.Verifier.VerifySCTSignature(sct, entry)
 }