diff --git a/libdevcore/Log.cpp b/libdevcore/Log.cpp
index 3dd2b3879..f28a2c6b9 100644
--- a/libdevcore/Log.cpp
+++ b/libdevcore/Log.cpp
@@ -33,7 +33,29 @@ using namespace dev;
 
 // Logging
 int dev::g_logVerbosity = 5;
-map<type_info const*, bool> dev::g_logOverride;
+mutex x_logOverride;
+
+/// Map of Log Channel types to bool, false forces the channel to be disabled, true forces it to be enabled.
+/// If a channel has no entry, then it will output as long as its verbosity (LogChannel::verbosity) is less than
+/// or equal to the currently output verbosity (g_logVerbosity).
+static map<type_info const*, bool> s_logOverride;
+
+LogOverrideAux::LogOverrideAux(std::type_info const* _ch, bool _value):
+	m_ch(_ch)
+{
+	Guard l(x_logOverride);
+	m_old = s_logOverride.count(_ch) ? (int)s_logOverride[_ch] : c_null;
+	s_logOverride[m_ch] = _value;
+}
+
+LogOverrideAux::~LogOverrideAux()
+{
+	Guard l(x_logOverride);
+	if (m_old == c_null)
+		s_logOverride.erase(m_ch);
+	else
+		s_logOverride[m_ch] = (bool)m_old;
+}
 
 #ifdef _WIN32
 const char* LogChannel::name() { return EthGray "..."; }
@@ -55,8 +77,9 @@ LogOutputStreamBase::LogOutputStreamBase(char const* _id, std::type_info const*
 	m_autospacing(_autospacing),
 	m_verbosity(_v)
 {
-	auto it = g_logOverride.find(_info);
-	if ((it != g_logOverride.end() && it->second == true) || (it == g_logOverride.end() && (int)_v <= g_logVerbosity))
+	Guard l(x_logOverride);
+	auto it = s_logOverride.find(_info);
+	if ((it != s_logOverride.end() && it->second == true) || (it == s_logOverride.end() && (int)_v <= g_logVerbosity))
 	{
 		time_t rawTime = std::chrono::system_clock::to_time_t(std::chrono::system_clock::now());
 		char buf[24];
diff --git a/libdevcore/Log.h b/libdevcore/Log.h
index 57d8cd349..ce0db17fe 100644
--- a/libdevcore/Log.h
+++ b/libdevcore/Log.h
@@ -54,10 +54,24 @@ extern int g_logVerbosity;
 /// The current method that the logging system uses to output the log messages. Defaults to simpleDebugOut().
 extern std::function<void(std::string const&, char const*)> g_logPost;
 
-/// Map of Log Channel types to bool, false forces the channel to be disabled, true forces it to be enabled.
-/// If a channel has no entry, then it will output as long as its verbosity (LogChannel::verbosity) is less than
-/// or equal to the currently output verbosity (g_logVerbosity).
-extern std::map<std::type_info const*, bool> g_logOverride;
+class LogOverrideAux
+{
+protected:
+	LogOverrideAux(std::type_info const* _ch, bool _value);
+	~LogOverrideAux();
+
+private:
+	std::type_info const* m_ch;
+	static const int c_null = -1;
+	int m_old;
+};
+
+template <class Channel>
+class LogOverride: LogOverrideAux
+{
+public:
+	LogOverride(bool _value): LogOverrideAux(&typeid(Channel), _value) {}
+};
 
 /// Temporary changes system's verbosity for specific function. Restores the old verbosity when function returns.
 /// Not thread-safe, use with caution!
diff --git a/libethereum/State.cpp b/libethereum/State.cpp
index 09765d9ee..f84ee819f 100644
--- a/libethereum/State.cpp
+++ b/libethereum/State.cpp
@@ -592,24 +592,6 @@ string State::vmTrace(bytesConstRef _block, BlockChain const& _bc, ImportRequire
 	return ss.str();
 }
 
-template <class Channel>
-class LogOverride
-{
-public:
-	LogOverride(bool _value): m_old(g_logOverride.count(&typeid(Channel)) ? (int)g_logOverride[&typeid(Channel)] : c_null) { g_logOverride[&typeid(Channel)] = _value; }
-	~LogOverride()
-	{
-		if (m_old == c_null)
-			g_logOverride.erase(&typeid(Channel));
-		else
-			g_logOverride[&typeid(Channel)] = (bool)m_old;
-	}
-
-private:
-	static const int c_null = -1;
-	int m_old;
-};
-
 u256 State::enact(bytesConstRef _block, BlockChain const& _bc, ImportRequirements::value _ir)
 {
 	// m_currentBlock is assumed to be prepopulated and reset.