diff --git a/libweb3jsonrpc/WebThreeStubServerBase.cpp b/libweb3jsonrpc/WebThreeStubServerBase.cpp
index bd09ac9c6..d6f00f7cb 100644
--- a/libweb3jsonrpc/WebThreeStubServerBase.cpp
+++ b/libweb3jsonrpc/WebThreeStubServerBase.cpp
@@ -583,8 +583,7 @@ Json::Value WebThreeStubServerBase::shh_changed(int const& _id)
 			else
 			{
 				unsigned i = 0;
-				for (; i < face()->getFilter(_id).size() && !face()->getFilter(_id)[i]; ++i) {}
-				m = e.open(face()->getFilter(_id)[i], i);
+				m = e.open(face()->filterKey(_id));
 			}
 			ret.append(toJson(h, e, m));
 		}
diff --git a/libwhisper/Interface.h b/libwhisper/Interface.h
index 1ee36c756..2a14b4a16 100644
--- a/libwhisper/Interface.h
+++ b/libwhisper/Interface.h
@@ -45,10 +45,18 @@ namespace shh
 
 class Watch;
 
+struct FilterKey
+{
+	unsigned topicIndex = (unsigned)-1;
+	Secret key;
+};
+
 struct InstalledFilter
 {
 	InstalledFilter(FullTopic const& _f): full(_f), filter(_f) {}
 
+	FilterKey filterKey() const { unsigned i; for (i = 0; i < full.size() && !full[i]; ++i) {} return i < full.size() ? FilterKey{i, full[i]} : FilterKey(); }
+
 	FullTopic full;
 	TopicFilter filter;
 	unsigned refCount = 1;
@@ -70,7 +78,7 @@ public:
 
 	virtual void inject(Envelope const& _m, WhisperPeer* _from = nullptr) = 0;
 
-	virtual FullTopic getFilter(unsigned _id) const = 0;
+	virtual FilterKey filterKey(unsigned _id) const = 0;
 	virtual unsigned installWatch(FullTopic const& _mask) = 0;
 	virtual unsigned installWatchOnId(h256 _filterId) = 0;
 	virtual void uninstallWatch(unsigned _watchId) = 0;
diff --git a/libwhisper/Message.h b/libwhisper/Message.h
index b23e5d576..0eef832eb 100644
--- a/libwhisper/Message.h
+++ b/libwhisper/Message.h
@@ -45,6 +45,8 @@ enum IncludeNonce
 	WithNonce = 1
 };
 
+static const unsigned NotPublic = (unsigned)-1;
+
 class Envelope
 {
 	friend class Message;
@@ -64,7 +66,7 @@ public:
 	Topic const& topic() const { return m_topic; }
 	bytes const& data() const { return m_data; }
 
-	Message open(Secret const& _s = Secret(), unsigned _topicIndex = (unsigned)-1) const;
+	Message open(Secret const& _s, unsigned _topicIndex = NotPublic) const;
 
 	unsigned workProved() const;
 	void proveWork(unsigned _ms);
@@ -85,8 +87,6 @@ enum /*Message Flags*/
 	ContainsSignature = 1
 };
 
-static const unsigned NotPublic = (unsigned)-1;
-
 /// An (unencrypted) message, constructed from the combination of an Envelope, and, potentially,
 /// a Secret key to decrypt the Message.
 class Message
diff --git a/libwhisper/WhisperHost.h b/libwhisper/WhisperHost.h
index 07207989e..425fe3108 100644
--- a/libwhisper/WhisperHost.h
+++ b/libwhisper/WhisperHost.h
@@ -51,7 +51,7 @@ public:
 
 	virtual void inject(Envelope const& _e, WhisperPeer* _from = nullptr) override;
 
-	virtual FullTopic getFilter(unsigned _id) const { try { return m_filters.at(m_watches.at(_id).id).full; } catch (...) { return FullTopic(); } }
+	virtual FilterKey filterKey(unsigned _id) const { try { return m_filters.at(m_watches.at(_id).id).filterKey(); } catch (...) { return FilterKey(); } }
 	virtual unsigned installWatch(FullTopic const& _filter) override;
 	virtual unsigned installWatchOnId(h256 _filterId) override;
 	virtual void uninstallWatch(unsigned _watchId) override;
diff --git a/test/whisperTopic.cpp b/test/whisperTopic.cpp
index 31cefdb8a..a47b0a574 100644
--- a/test/whisperTopic.cpp
+++ b/test/whisperTopic.cpp
@@ -55,7 +55,7 @@ BOOST_AUTO_TEST_CASE(topic)
 		{
 			for (auto i: wh->checkWatch(w))
 			{
-				Message msg = wh->envelope(i).open();
+				Message msg = wh->envelope(i).open(wh->filterKey());
 				last = RLP(msg.payload()).toInt<unsigned>();
 				cnote << "New message from:" << msg.from().abridged() << RLP(msg.payload()).toInt<unsigned>();
 				result += last;