diff --git a/interface/src/main.cpp b/interface/src/main.cpp
index 27eb296784..3b23db079b 100644
--- a/interface/src/main.cpp
+++ b/interface/src/main.cpp
@@ -867,12 +867,14 @@ void display(void)
 		
         //  Render avatars of other agents
         AgentList* agentList = AgentList::getInstance();
+        agentList->lock();
         for (AgentList::iterator agent = agentList->begin(); agent != agentList->end(); agent++) {
             if (agent->getLinkedData() != NULL && agent->getType() == AGENT_TYPE_AVATAR) {
                 Avatar *avatar = (Avatar *)agent->getLinkedData();
                 avatar->render(0);
             }
         }
+        agentList->unlock();
         
         //  Render the world box
         if (!::lookingInMirror && ::statsOn) { render_world_box(); }
@@ -1486,12 +1488,14 @@ void idle(void) {
 		
         //loop through all the other avatars and simulate them...
         AgentList* agentList = AgentList::getInstance();
+        agentList->lock();
         for(AgentList::iterator agent = agentList->begin(); agent != agentList->end(); agent++) {
             if (agent->getLinkedData() != NULL) {
                 Avatar *avatar = (Avatar *)agent->getLinkedData();
                 avatar->simulate(deltaTime);
             }
         }
+        agentList->unlock();
     
         myAvatar.simulate(deltaTime);
 
diff --git a/libraries/shared/src/AgentList.cpp b/libraries/shared/src/AgentList.cpp
index 2c7d6cf25d..b05c4558d3 100644
--- a/libraries/shared/src/AgentList.cpp
+++ b/libraries/shared/src/AgentList.cpp
@@ -66,7 +66,7 @@ AgentList::AgentList(char newOwnerType, unsigned int newSocketListenPort) :
     socketListenPort(newSocketListenPort),
     lastAgentId(0)
 {
-
+    pthread_mutex_init(&mutex, 0);
 }
 
 AgentList::~AgentList() {
@@ -74,6 +74,8 @@ AgentList::~AgentList() {
     stopSilentAgentRemovalThread();
     stopDomainServerCheckInThread();
     stopPingUnknownAgentsThread();
+    
+    pthread_mutex_destroy(&mutex);
 }
 
 UDPSocket& AgentList::getAgentSocket() {
@@ -106,6 +108,8 @@ void AgentList::processAgentData(sockaddr *senderAddress, unsigned char *packetD
 }
 
 void AgentList::processBulkAgentData(sockaddr *senderAddress, unsigned char *packetData, int numTotalBytes) {
+    lock();
+    
     // find the avatar mixer in our agent list and update the lastRecvTime from it
     Agent* bulkSendAgent = agentWithAddress(senderAddress);
 
@@ -141,6 +145,8 @@ void AgentList::processBulkAgentData(sockaddr *senderAddress, unsigned char *pac
                                                packetHolder,
                                                numTotalBytes - (currentPosition - startPosition));
     }
+    
+    unlock();
 }
 
 int AgentList::updateAgentWithData(sockaddr *senderAddress, unsigned char *packetData, size_t dataBytes) {
diff --git a/libraries/shared/src/AgentList.h b/libraries/shared/src/AgentList.h
index 19dee70359..1a7a99b751 100644
--- a/libraries/shared/src/AgentList.h
+++ b/libraries/shared/src/AgentList.h
@@ -53,6 +53,9 @@ public:
     uint16_t getLastAgentId();
     void increaseAgentId();
     
+    void lock() { pthread_mutex_lock(&mutex); }
+    void unlock() { pthread_mutex_unlock(&mutex); }
+    
     int updateList(unsigned char *packetData, size_t dataBytes);
     
     Agent* agentWithAddress(sockaddr *senderAddress);
@@ -99,6 +102,7 @@ private:
     pthread_t removeSilentAgentsThread;
     pthread_t checkInWithDomainServerThread;
     pthread_t pingUnknownAgentsThread;
+    pthread_mutex_t mutex;
     
     void handlePingReply(sockaddr *agentAddress);
 };