diff --git a/src/cpp/ripple/LedgerAcquire.cpp b/src/cpp/ripple/LedgerAcquire.cpp
index 352b1d2206..5d1e7c96e2 100644
--- a/src/cpp/ripple/LedgerAcquire.cpp
+++ b/src/cpp/ripple/LedgerAcquire.cpp
@@ -71,6 +71,8 @@ void PeerSet::TimerEntry(boost::weak_ptr<PeerSet> wptr, const boost::system::err
 {
 	if (result == boost::asio::error::operation_aborted)
 		return;
+
+	ScopedLock sl(theApp->getMasterLock());
 	boost::shared_ptr<PeerSet> ptr = wptr.lock();
 	if (ptr)
 		ptr->invokeOnTimer();