diff --git a/include/TNetwork.h b/include/TNetwork.h
index 3b4980e..5ccb8b2 100644
--- a/include/TNetwork.h
+++ b/include/TNetwork.h
@@ -37,6 +37,7 @@ private:
     TResourceManager& mResourceManager;
     std::thread mUDPThread;
     std::thread mTCPThread;
+    std::mutex mOpenIDMutex;
 
     std::vector<uint8_t> UDPRcvFromClient(ip::udp::endpoint& ClientEndpoint);
     void HandleDownload(TConnection&& TCPSock);
diff --git a/src/TNetwork.cpp b/src/TNetwork.cpp
index 5a48c46..5e7444c 100644
--- a/src/TNetwork.cpp
+++ b/src/TNetwork.cpp
@@ -577,6 +577,10 @@ void TNetwork::OnDisconnect(const std::weak_ptr<TClient>& ClientPtr) {
 }
 
 int TNetwork::OpenID() {
+    // This lock ensures that each call to OpenID is exclusive.
+    // If we didn't have this, two concurrent calls to this function may result
+    // in the same ID.
+    std::unique_lock Lock(mOpenIDMutex);
     int ID = 0;
     bool found;
     do {