diff --git a/libi2pd/SSU.cpp b/libi2pd/SSU.cpp
index 9e814303..be263370 100644
--- a/libi2pd/SSU.cpp
+++ b/libi2pd/SSU.cpp
@@ -218,7 +218,7 @@ namespace transport
 
 	void SSUServer::AddRelay (uint32_t tag, std::shared_ptr<SSUSession> relay)
 	{
-		m_Relays[tag] = relay;
+		m_Relays.emplace (tag, relay);
 	}
 
 	void SSUServer::RemoveRelay (uint32_t tag)
diff --git a/libi2pd/SSU.h b/libi2pd/SSU.h
index b97cacb4..4b561be0 100644
--- a/libi2pd/SSU.h
+++ b/libi2pd/SSU.h
@@ -139,7 +139,7 @@ namespace transport
 			std::list<boost::asio::ip::udp::endpoint> m_Introducers, m_IntroducersV6; // introducers we are connected to
 			std::map<boost::asio::ip::udp::endpoint, std::shared_ptr<SSUSession> > m_Sessions, m_SessionsV6;
 			std::map<uint32_t, std::shared_ptr<SSUSession> > m_Relays; // we are introducer
-			std::map<uint32_t, PeerTest> m_PeerTests; // nonce -> creation time in milliseconds
+			boost::container::flat_map<uint32_t, PeerTest> m_PeerTests; // nonce -> creation time in milliseconds
 
 			i2p::util::MemoryPool<Fragment> m_FragmentsPool;
 			i2p::util::MemoryPool<IncompleteMessage> m_IncompleteMessagesPool;
diff --git a/libi2pd/SSUData.cpp b/libi2pd/SSUData.cpp
index 18621fe0..ccc89b41 100644
--- a/libi2pd/SSUData.cpp
+++ b/libi2pd/SSUData.cpp
@@ -310,7 +310,7 @@ namespace transport
 		if (m_SentMessages.empty ()) // schedule resend at first message only
 			ScheduleResend ();
 
-		auto ret = m_SentMessages.insert (std::make_pair (msgID, m_Session.GetServer ().GetSentMessagesPool ().AcquireShared ()));
+		auto ret = m_SentMessages.emplace (msgID, m_Session.GetServer ().GetSentMessagesPool ().AcquireShared ());
 		auto& sentMessage = ret.first->second;
 		if (ret.second)
 		{
diff --git a/libi2pd/SSUData.h b/libi2pd/SSUData.h
index 35311bb6..fa6aa92c 100644
--- a/libi2pd/SSUData.h
+++ b/libi2pd/SSUData.h
@@ -11,10 +11,10 @@
 
 #include <inttypes.h>
 #include <string.h>
-#include <unordered_map>
 #include <vector>
 #include <memory>
 #include <boost/asio.hpp>
+#include <boost/container/flat_map.hpp>
 #include "I2NPProtocol.h"
 #include "Identity.h"
 #include "RouterInfo.h"
@@ -123,9 +123,9 @@ namespace transport
 		private:
 
 			SSUSession& m_Session;
-			std::unordered_map<uint32_t, std::shared_ptr<IncompleteMessage> > m_IncompleteMessages;
-			std::unordered_map<uint32_t, std::shared_ptr<SentMessage> > m_SentMessages;
-			std::unordered_map<uint32_t, uint64_t> m_ReceivedMessages; // msgID -> timestamp in seconds
+			boost::container::flat_map<uint32_t, std::shared_ptr<IncompleteMessage> > m_IncompleteMessages;
+			boost::container::flat_map<uint32_t, std::shared_ptr<SentMessage> > m_SentMessages;
+			boost::container::flat_map<uint32_t, uint64_t> m_ReceivedMessages; // msgID -> timestamp in seconds
 			boost::asio::deadline_timer m_ResendTimer;
 			int m_MaxPacketSize, m_PacketSize;
 			i2p::I2NPMessagesHandler m_Handler;