diff --git a/whisperv6/envelope.go b/whisperv6/envelope.go
index 2c80d47..2f947f1 100644
--- a/whisperv6/envelope.go
+++ b/whisperv6/envelope.go
@@ -208,6 +208,10 @@ func (e *Envelope) OpenSymmetric(key []byte) (msg *ReceivedMessage, err error) {
 
 // Open tries to decrypt an envelope, and populates the message fields in case of success.
 func (e *Envelope) Open(watcher *Filter) (msg *ReceivedMessage) {
+	if watcher == nil {
+		return nil
+	}
+
 	// The API interface forbids filters doing both symmetric and asymmetric encryption.
 	if watcher.expectsAsymmetricEncryption() && watcher.expectsSymmetricEncryption() {
 		return nil