diff --git a/cmd/common.go b/cmd/common.go
index 6aac0b2..3cddc6d 100644
--- a/cmd/common.go
+++ b/cmd/common.go
@@ -108,7 +108,7 @@ func makeLogHandle(logInfo *certspotter.LogInfo) (*logHandle, error) {
 	if err != nil {
 		return nil, fmt.Errorf("Bad public key: %s", err)
 	}
-	ctlog.scanner = certspotter.NewScanner(logInfo.FullURI(), logKey, &certspotter.ScannerOptions{
+	ctlog.scanner = certspotter.NewScanner(logInfo.FullURI(), logInfo.ID(), logKey, &certspotter.ScannerOptions{
 		BatchSize:  *batchSize,
 		NumWorkers: *numWorkers,
 		Quiet:      !*verbose,
diff --git a/scanner.go b/scanner.go
index 41ba6da..462fa78 100644
--- a/scanner.go
+++ b/scanner.go
@@ -62,6 +62,7 @@ type Scanner struct {
 
 	// Public key of the log
 	publicKey crypto.PublicKey
+	LogId []byte
 
 	// Client used to talk to the CT log instance
 	logClient *client.LogClient
@@ -208,6 +209,7 @@ func (s *Scanner) GetSTH() (*ct.SignedTreeHead, error) {
 			return nil, errors.New("STH signature is invalid: " + err.Error())
 		}
 	}
+	copy(latestSth.LogID[:], s.LogId)
 	return latestSth, nil
 }
 
@@ -312,9 +314,10 @@ func (s *Scanner) Scan(startIndex int64, endIndex int64, processCert ProcessCall
 
 // Creates a new Scanner instance using |client| to talk to the log, and taking
 // configuration options from |opts|.
-func NewScanner(logUri string, publicKey crypto.PublicKey, opts *ScannerOptions) *Scanner {
+func NewScanner(logUri string, logId []byte, publicKey crypto.PublicKey, opts *ScannerOptions) *Scanner {
 	var scanner Scanner
 	scanner.LogUri = logUri
+	scanner.LogId = logId
 	scanner.publicKey = publicKey
 	scanner.logClient = client.New(logUri)
 	scanner.opts = *opts