diff --git a/whisper/whisperv5/api.go b/whisper/whisperv5/api.go
index 96c4b0e6c4..7fd76ee5b0 100644
--- a/whisper/whisperv5/api.go
+++ b/whisper/whisperv5/api.go
@@ -562,7 +562,7 @@ func (api *PublicWhisperAPI) NewMessageFilter(req Criteria) (string, error) {
 	}
 
 	if len(req.Topics) > 0 {
-		topics = make([][]byte, 1)
+		topics = make([][]byte, 0, 1)
 		for _, topic := range req.Topics {
 			topics = append(topics, topic[:])
 		}
diff --git a/whisper/whisperv6/api.go b/whisper/whisperv6/api.go
index 3dddb69539..0cfab7cba2 100644
--- a/whisper/whisperv6/api.go
+++ b/whisper/whisperv6/api.go
@@ -562,7 +562,7 @@ func (api *PublicWhisperAPI) NewMessageFilter(req Criteria) (string, error) {
 	}
 
 	if len(req.Topics) > 0 {
-		topics = make([][]byte, 1)
+		topics = make([][]byte, 0, 1)
 		for _, topic := range req.Topics {
 			topics = append(topics, topic[:])
 		}