diff --git a/cttypes/sth.go b/cttypes/sth.go
index 880e7da..aec9d2a 100644
--- a/cttypes/sth.go
+++ b/cttypes/sth.go
@@ -31,3 +31,7 @@ type GossipedSignedTreeHead struct {
 func (sth *SignedTreeHead) TimestampTime() time.Time {
 	return time.UnixMilli(int64(sth.Timestamp))
 }
+
+func (sth *SignedTreeHead) Same(other *SignedTreeHead) bool {
+	return sth.TreeSize == other.TreeSize && sth.Timestamp == other.Timestamp && sth.RootHash == other.RootHash
+}
diff --git a/monitor/monitor.go b/monitor/monitor.go
index 1e41eaa..14cad2e 100644
--- a/monitor/monitor.go
+++ b/monitor/monitor.go
@@ -357,7 +357,7 @@ func newBatch(number uint64, begin uint64, sths []*StoredSTH, downloadJobSize ui
 func appendSTH(sths []*StoredSTH, sth *StoredSTH) []*StoredSTH {
 	i := len(sths)
 	for i > 0 {
-		if sths[i-1].TreeSize == sth.TreeSize && sths[i-1].RootHash == sth.RootHash {
+		if sths[i-1].Same(&sth.SignedTreeHead) {
 			return sths
 		}
 		if sths[i-1].TreeSize < sth.TreeSize {