diff --git a/CMakeLists.txt b/CMakeLists.txt
index 25ed3a7..0b199ba 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,6 +1,6 @@
 cmake_minimum_required(VERSION 3.7)
 project(libdatachannel
-	VERSION 0.13.1
+	VERSION 0.13.2
 	LANGUAGES CXX)
 set(PROJECT_DESCRIPTION "WebRTC Data Channels Library")
 
diff --git a/src/candidate.cpp b/src/candidate.cpp
index c856aa4..3236375 100644
--- a/src/candidate.cpp
+++ b/src/candidate.cpp
@@ -93,7 +93,7 @@ void Candidate::parse(string candidate) {
 	                                        {"so", TransportType::TcpSo}};
 
 	const std::array prefixes{"a=", "candidate:"};
-	for (const string &prefix : prefixes)
+	for (string prefix : prefixes)
 		if (match_prefix(candidate, prefix))
 			candidate.erase(0, prefix.size());
 
diff --git a/src/impl/sctptransport.cpp b/src/impl/sctptransport.cpp
index ddcaedf..7ee318d 100644
--- a/src/impl/sctptransport.cpp
+++ b/src/impl/sctptransport.cpp
@@ -85,8 +85,30 @@ static LogCounter
 static LogCounter COUNTER_BAD_SCTP_STATUS(plog::warning,
                                           "Number of SCTP packets received with a bad status");
 
-std::unordered_set<SctpTransport *> SctpTransport::Instances;
-std::shared_mutex SctpTransport::InstancesMutex;
+class SctpTransport::InstancesSet {
+public:
+	void insert(SctpTransport *instance) {
+		std::unique_lock lock(mMutex);
+		mSet.insert(instance);
+	}
+
+	void erase(SctpTransport *instance) {
+		std::unique_lock lock(mMutex);
+		mSet.erase(instance);
+	}
+
+	using shared_lock = std::shared_lock<std::shared_mutex>;
+	optional<shared_lock> lock(SctpTransport *instance) {
+		shared_lock lock(mMutex);
+		return mSet.find(instance) != mSet.end() ? std::make_optional(std::move(lock)) : nullopt;
+	}
+
+private:
+	std::unordered_set<SctpTransport *> mSet;
+	std::shared_mutex mMutex;
+};
+
+SctpTransport::InstancesSet *SctpTransport::Instances = new InstancesSet;
 
 void SctpTransport::Init() {
 	usrsctp_init(0, &SctpTransport::WriteCallback, nullptr);
@@ -159,10 +181,7 @@ SctpTransport::SctpTransport(shared_ptr<Transport> lower, const Configuration &c
 	PLOG_DEBUG << "Initializing SCTP transport";
 
 	usrsctp_register_address(this);
-	{
-		std::unique_lock lock(InstancesMutex);
-		Instances.insert(this);
-	}
+	Instances->insert(this);
 
 	mSock = usrsctp_socket(AF_CONN, SOCK_STREAM, IPPROTO_SCTP, nullptr, nullptr, 0, nullptr);
 	if (!mSock)
@@ -301,10 +320,7 @@ SctpTransport::~SctpTransport() {
 	close();
 
 	usrsctp_deregister_address(this);
-	{
-		std::unique_lock lock(InstancesMutex);
-		Instances.erase(this);
-	}
+	Instances->erase(this);
 }
 
 void SctpTransport::start() {
@@ -864,11 +880,8 @@ optional<milliseconds> SctpTransport::rtt() {
 void SctpTransport::UpcallCallback(struct socket *, void *arg, int /* flags */) {
 	auto *transport = static_cast<SctpTransport *>(arg);
 
-	std::shared_lock lock(InstancesMutex);
-	if (Instances.find(transport) == Instances.end())
-		return;
-
-	transport->handleUpcall();
+	if(auto lock = Instances->lock(transport))
+		transport->handleUpcall();
 }
 
 int SctpTransport::WriteCallback(void *ptr, void *data, size_t len, uint8_t tos, uint8_t set_df) {
@@ -876,11 +889,10 @@ int SctpTransport::WriteCallback(void *ptr, void *data, size_t len, uint8_t tos,
 
 	// Workaround for sctplab/usrsctp#405: Send callback is invoked on already closed socket
 	// https://github.com/sctplab/usrsctp/issues/405
-	std::shared_lock lock(InstancesMutex);
-	if (Instances.find(transport) == Instances.end())
+	if(auto lock = Instances->lock(transport))
+		return transport->handleWrite(static_cast<byte *>(data), len, tos, set_df);
+	else
 		return -1;
-
-	return transport->handleWrite(static_cast<byte *>(data), len, tos, set_df);
 }
 
 } // namespace rtc::impl
diff --git a/src/impl/sctptransport.hpp b/src/impl/sctptransport.hpp
index a7cf7b2..654099b 100644
--- a/src/impl/sctptransport.hpp
+++ b/src/impl/sctptransport.hpp
@@ -120,8 +120,8 @@ private:
 	static void UpcallCallback(struct socket *sock, void *arg, int flags);
 	static int WriteCallback(void *sctp_ptr, void *data, size_t len, uint8_t tos, uint8_t set_df);
 
-	static std::unordered_set<SctpTransport *> Instances;
-	static std::shared_mutex InstancesMutex;
+	class InstancesSet;
+	static InstancesSet *Instances;
 };
 
 } // namespace rtc::impl