diff --git a/whisper/topic.go b/whisper/topic.go
index 7c26cfba9..a965c7cc2 100644
--- a/whisper/topic.go
+++ b/whisper/topic.go
@@ -52,7 +52,7 @@ func (self *Topic) String() string {
 type topicSet map[string]struct{}
 
 // NewTopicSet creates a topic hash set from a slice of topics.
-func NewTopicSet(topics []Topic) topicSet {
+func newTopicSet(topics []Topic) topicSet {
 	set := make(map[string]struct{})
 	for _, topic := range topics {
 		set[topic.String()] = struct{}{}
diff --git a/whisper/topic_test.go b/whisper/topic_test.go
index 5f8583987..4015079dc 100644
--- a/whisper/topic_test.go
+++ b/whisper/topic_test.go
@@ -57,7 +57,7 @@ func TestTopicSetCreation(t *testing.T) {
 	for i, tt := range topicCreationTests {
 		topics[i] = NewTopic(tt.data)
 	}
-	set := NewTopicSet(topics)
+	set := newTopicSet(topics)
 	for i, tt := range topicCreationTests {
 		topic := NewTopic(tt.data)
 		if _, ok := set[topic.String()]; !ok {
diff --git a/whisper/whisper.go b/whisper/whisper.go
index 48efff622..9317fad50 100644
--- a/whisper/whisper.go
+++ b/whisper/whisper.go
@@ -119,7 +119,7 @@ func (self *Whisper) Watch(options Filter) int {
 	filter := filter.Generic{
 		Str1: string(crypto.FromECDSAPub(options.To)),
 		Str2: string(crypto.FromECDSAPub(options.From)),
-		Data: NewTopicSet(options.Topics),
+		Data: newTopicSet(options.Topics),
 		Fn: func(data interface{}) {
 			options.Fn(data.(*Message))
 		},
@@ -281,7 +281,7 @@ func createFilter(message *Message, topics []Topic) filter.Filter {
 	return filter.Generic{
 		Str1: string(crypto.FromECDSAPub(message.To)),
 		Str2: string(crypto.FromECDSAPub(message.Recover())),
-		Data: NewTopicSet(topics),
+		Data: newTopicSet(topics),
 	}
 }