diff --git a/src/cpp/ripple/Application.h b/src/cpp/ripple/Application.h
index a100190966..3e68a8b14a 100644
--- a/src/cpp/ripple/Application.h
+++ b/src/cpp/ripple/Application.h
@@ -43,6 +43,8 @@ class Application
 	boost::asio::io_service			mIOService, mAuxService;
 	boost::asio::io_service::work	mIOWork, mAuxWork;
 
+	boost::recursive_mutex	mMasterLock;
+
 	Wallet					mWallet;
 	UniqueNodeList			mUNL;
 	LedgerMaster			mMasterLedger;
@@ -99,6 +101,7 @@ public:
 	JobQueue& getJobQueue()							{ return mJobQueue; }
 	SuppressionTable& getSuppression()				{ return mSuppressions; }
 	RPCHandler& getRPCHandler()						{ return mRPCHandler; }
+	boost::recursive_mutex& getMasterLock()			{ return mMasterLock; }
 
 
 	bool isNew(const uint256& s)					{ return mSuppressions.addSuppression(s); }
diff --git a/src/cpp/ripple/LedgerConsensus.cpp b/src/cpp/ripple/LedgerConsensus.cpp
index 0fc07a4aad..9f9e099454 100644
--- a/src/cpp/ripple/LedgerConsensus.cpp
+++ b/src/cpp/ripple/LedgerConsensus.cpp
@@ -1141,6 +1141,7 @@ uint32 LedgerConsensus::roundCloseTime(uint32 closeTime)
 
 void LedgerConsensus::accept(SHAMap::ref set)
 {
+	boost::recursive_mutex::scoped_lock masterLock(theApp->getMasterLock());
 	assert(set->getHash() == mOurPosition->getCurrentHash());
 
 	uint32 closeTime = roundCloseTime(mOurPosition->getCloseTime());
diff --git a/src/cpp/ripple/NetworkOPs.cpp b/src/cpp/ripple/NetworkOPs.cpp
index 44259523f6..882551cc81 100644
--- a/src/cpp/ripple/NetworkOPs.cpp
+++ b/src/cpp/ripple/NetworkOPs.cpp
@@ -161,7 +161,6 @@ Transaction::pointer NetworkOPs::submitTransactionSync(const Transaction::pointe
 
 Transaction::pointer NetworkOPs::processTransaction(Transaction::pointer trans, stCallback callback)
 {
-	Transaction::pointer dbtx = theApp->getMasterTransaction().fetch(trans->getID(), true);
 
 	int newFlags = theApp->getSuppression().getFlags(trans->getID());
 	if ((newFlags & SF_BAD) != 0)
@@ -182,6 +181,8 @@ Transaction::pointer NetworkOPs::processTransaction(Transaction::pointer trans,
 		theApp->isNewFlag(trans->getID(), SF_SIGGOOD);
 	}
 
+	boost::recursive_mutex::scoped_lock sl(theApp->getMasterLock());
+	Transaction::pointer dbtx = theApp->getMasterTransaction().fetch(trans->getID(), true);
 	TER r = mLedgerMaster->doTransaction(*trans->getSTransaction(), tapOPEN_LEDGER | tapNO_CHECK_SIGN);
 	trans->setResult(r);
 
@@ -762,6 +763,8 @@ uint256 NetworkOPs::getConsensusLCL()
 void NetworkOPs::processTrustedProposal(LedgerProposal::pointer proposal,
 	boost::shared_ptr<ripple::TMProposeSet> set, RippleAddress nodePublic, uint256 checkLedger, bool sigGood)
 {
+	boost::recursive_mutex::scoped_lock sl(theApp->getMasterLock());
+
 	bool relay = true;
 
 	if (!haveConsensusObject())
diff --git a/src/cpp/ripple/Peer.cpp b/src/cpp/ripple/Peer.cpp
index a5f34665f6..f364df838b 100644
--- a/src/cpp/ripple/Peer.cpp
+++ b/src/cpp/ripple/Peer.cpp
@@ -41,6 +41,8 @@ void Peer::handle_write(const boost::system::error_code& error, size_t bytes_tra
 //		std::cerr << "Peer::handle_write bytes: "<< bytes_transferred << std::endl;
 #endif
 
+	boost::recursive_mutex::scoped_lock sl(theApp->getMasterLock());
+
 	mSendingPacket.reset();
 
 	if (mDetaching)
@@ -357,6 +359,7 @@ void Peer::handle_read_body(const boost::system::error_code& error)
 	else
 	{
 		cLog(lsINFO) << "Peer: Body: Error: " << ADDRESS(this) << ": " << error.category().name() << ": " << error.message() << ": " << error;
+		boost::recursive_mutex::scoped_lock sl(theApp->getMasterLock());
 		detach("hrb");
 	}
 }
@@ -371,6 +374,7 @@ void Peer::processReadBuffer()
 //	std::cerr << "Peer::processReadBuffer: " << mIpPort.first << " " << mIpPort.second << std::endl;
 
 	// If connected and get a mtHELLO or if not connected and get a non-mtHELLO, wrong message was sent.
+	boost::recursive_mutex::scoped_lock sl(theApp->getMasterLock());
 	if (mHelloed == (type == ripple::mtHELLO))
 	{
 		cLog(lsWARNING) << "Wrong message type: " << type;
diff --git a/src/cpp/ripple/RPCHandler.cpp b/src/cpp/ripple/RPCHandler.cpp
index bd70776c40..fbd24d555f 100644
--- a/src/cpp/ripple/RPCHandler.cpp
+++ b/src/cpp/ripple/RPCHandler.cpp
@@ -1384,7 +1384,9 @@ Json::Value RPCHandler::doCommand(const std::string& command, Json::Value& param
 		return rpcError(rpcNO_NETWORK);
 	}
 	// XXX Should verify we have a current ledger.
-	else if ((commandsA[i].iOptions & optCurrent) && false)
+
+	boost::recursive_mutex::scoped_lock sl(theApp->getMasterLock());
+	if ((commandsA[i].iOptions & optCurrent) && false)
 	{
 		return rpcError(rpcNO_CURRENT);
 	}