diff --git a/libwhisper/Common.h b/libwhisper/Common.h
index 4f5bda540..ca84469ae 100644
--- a/libwhisper/Common.h
+++ b/libwhisper/Common.h
@@ -59,6 +59,7 @@ enum WhisperPacket
 };
 
 enum { TopicBloomFilterSize = 64 };
+enum { WhisperProtocolVersion = 2 };
 
 using AbridgedTopic = FixedHash<4>;
 using Topic = h256;
diff --git a/libwhisper/WhisperHost.h b/libwhisper/WhisperHost.h
index 69a1280aa..75ee15887 100644
--- a/libwhisper/WhisperHost.h
+++ b/libwhisper/WhisperHost.h
@@ -50,7 +50,7 @@ class WhisperHost: public HostCapability<WhisperPeer>, public Interface, public
 public:
 	WhisperHost();
 	virtual ~WhisperHost();
-	unsigned protocolVersion() const { return 2; }
+	unsigned protocolVersion() const { return WhisperProtocolVersion; }
 	void cleanup(); ///< remove old messages
 	std::map<h256, Envelope> all() const { dev::ReadGuard l(x_messages); return m_messages; }
 	FixedHash<TopicBloomFilterSize> bloom() const { dev::Guard l(m_filterLock); return m_bloom; }
diff --git a/libwhisper/WhisperPeer.cpp b/libwhisper/WhisperPeer.cpp
index ff73732ce..97b533bdf 100644
--- a/libwhisper/WhisperPeer.cpp
+++ b/libwhisper/WhisperPeer.cpp
@@ -117,10 +117,11 @@ void WhisperPeer::noteNewMessage(h256 _h, Envelope const& _m)
 
 void WhisperPeer::sendTopicsOfInterest(FixedHash<TopicBloomFilterSize> const& _bloom)
 {
+	Guard g(x_advertiseTopicsOfInterest);
 	RLPStream s;
 	prep(s, TopicFilterPacket, 1);
 	s << _bloom;
 	sealAndSend(s);
-
 	m_advertiseTopicsOfInterest = false;
 }
+
diff --git a/libwhisper/WhisperPeer.h b/libwhisper/WhisperPeer.h
index 9c242dc1f..1be2df97e 100644
--- a/libwhisper/WhisperPeer.h
+++ b/libwhisper/WhisperPeer.h
@@ -53,11 +53,11 @@ public:
 	virtual ~WhisperPeer();
 	WhisperHost* host() const;
 	static std::string name() { return "shh"; }
-	static u256 version() { return 3; }
+	static u256 version() { return WhisperProtocolVersion; }
 	static unsigned messageCount() { return PacketCount; }
 	FixedHash<TopicBloomFilterSize> bloom() const { dev::Guard g(x_bloom); return m_bloom; }
 	void sendTopicsOfInterest(FixedHash<TopicBloomFilterSize> const& _bloom); ///< sends our bloom filter to remote peer
-	void noteAdvertiseTopicsOfInterest() { m_advertiseTopicsOfInterest = true; }
+	void noteAdvertiseTopicsOfInterest() { dev::Guard g(x_advertiseTopicsOfInterest); m_advertiseTopicsOfInterest = true; }
 
 private:
 	virtual bool interpret(unsigned _id, RLP const&) override;
@@ -73,6 +73,7 @@ private:
 	mutable dev::Mutex x_bloom;
 	FixedHash<TopicBloomFilterSize> m_bloom; ///< Peer's topics of interest
 
+	mutable dev::Mutex x_advertiseTopicsOfInterest;
 	bool m_advertiseTopicsOfInterest;
 };