diff --git a/alethzero/Debugger.cpp b/alethzero/Debugger.cpp
index 14dcdb274..df3b9c301 100644
--- a/alethzero/Debugger.cpp
+++ b/alethzero/Debugger.cpp
@@ -348,7 +348,7 @@ void Debugger::on_dump_clicked()
 	ofstream f(fn.toStdString());
 	if (f.is_open())
 		for (WorldState const& ws: m_session.history)
-			f << ws.cur << " " << hex << toHex(dev::toCompactBigEndian(ws.curPC, 1)) << " " << hex << toHex(dev::toCompactBigEndian((int)(byte)ws.inst, 1)) << " " << hex << toHex(dev::toCompactBigEndian((uint64_t)ws.gas, 1)) << endl;
+			f << ws.cur << " " << hex << toHex(dev::toCompactBigEndian(ws.curPC, 1)) << " " << hex << toHex(dev::toCompactBigEndian((unsigned)(byte)ws.inst, 1)) << " " << hex << toHex(dev::toCompactBigEndian((uint64_t)ws.gas, 1)) << endl;
 }
 
 void Debugger::on_dumpPretty_clicked()
@@ -379,6 +379,6 @@ void Debugger::on_dumpStorage_clicked()
 			if (ws.inst == Instruction::STOP || ws.inst == Instruction::RETURN || ws.inst == Instruction::SUICIDE)
 				for (auto i: ws.storage)
 					f << toHex(dev::toCompactBigEndian(i.first, 1)) << " " << toHex(dev::toCompactBigEndian(i.second, 1)) << endl;
-			f << ws.cur << " " << hex << toHex(dev::toCompactBigEndian(ws.curPC, 1)) << " " << hex << toHex(dev::toCompactBigEndian((int)(byte)ws.inst, 1)) << " " << hex << toHex(dev::toCompactBigEndian((uint64_t)ws.gas, 1)) << endl;
+			f << ws.cur << " " << hex << toHex(dev::toCompactBigEndian(ws.curPC, 1)) << " " << hex << toHex(dev::toCompactBigEndian((unsigned)(byte)ws.inst, 1)) << " " << hex << toHex(dev::toCompactBigEndian((uint64_t)ws.gas, 1)) << endl;
 		}
 }
diff --git a/libdevcore/CommonData.h b/libdevcore/CommonData.h
index 5f4b0a39e..016faff6f 100644
--- a/libdevcore/CommonData.h
+++ b/libdevcore/CommonData.h
@@ -104,6 +104,7 @@ bytes asNibbles(bytesConstRef const& _s);
 template <class T, class Out>
 inline void toBigEndian(T _val, Out& o_out)
 {
+	static_assert(std::is_same<bigint, T>::value || !std::numeric_limits<T>::is_signed, "only unsigned types or bigint supported"); //bigint does not carry sign bit on shift
 	for (auto i = o_out.size(); i != 0; _val >>= 8, i--)
 	{
 		T v = _val & (T)0xff;
@@ -134,6 +135,7 @@ inline bytes toBigEndian(u160 _val) { bytes ret(20); toBigEndian(_val, ret); ret
 template <class T>
 inline bytes toCompactBigEndian(T _val, unsigned _min = 0)
 {
+	static_assert(std::is_same<bigint, T>::value || !std::numeric_limits<T>::is_signed, "only unsigned types or bigint supported"); //bigint does not carry sign bit on shift
 	int i = 0;
 	for (T v = _val; v; ++i, v >>= 8) {}
 	bytes ret(std::max<unsigned>(_min, i), 0);
@@ -150,6 +152,7 @@ inline bytes toCompactBigEndian(byte _val, unsigned _min = 0)
 template <class T>
 inline std::string toCompactBigEndianString(T _val, unsigned _min = 0)
 {
+	static_assert(std::is_same<bigint, T>::value || !std::numeric_limits<T>::is_signed, "only unsigned types or bigint supported"); //bigint does not carry sign bit on shift
 	int i = 0;
 	for (T v = _val; v; ++i, v >>= 8) {}
 	std::string ret(std::max<unsigned>(_min, i), '\0');
@@ -199,6 +202,7 @@ std::string randomWord();
 template <class T>
 inline unsigned bytesRequired(T _i)
 {
+	static_assert(std::is_same<bigint, T>::value || !std::numeric_limits<T>::is_signed, "only unsigned types or bigint supported"); //bigint does not carry sign bit on shift
 	unsigned i = 0;
 	for (; _i != 0; ++i, _i >>= 8) {}
 	return i;
diff --git a/mix/ContractCallDataEncoder.cpp b/mix/ContractCallDataEncoder.cpp
index ed215d342..29bcbba8e 100644
--- a/mix/ContractCallDataEncoder.cpp
+++ b/mix/ContractCallDataEncoder.cpp
@@ -104,7 +104,7 @@ void ContractCallDataEncoder::encode(QVariant const& _data, SolidityType const&
 		m_dynamicData += empty; //reserve space for count
 		encodeSingleItem(_data.toString(), _type, m_dynamicData);
 		vector_ref<byte> sizeRef(m_dynamicData.data() + sizePos, 32);
-		toBigEndian(_data.toString().size(), sizeRef);
+		toBigEndian(static_cast<unsigned>(_data.toString().size()), sizeRef);
 		m_staticOffsetMap.push_back(std::make_pair(m_encodedData.size(), sizePos));
 		m_encodedData += empty; //reserve space for offset
 	}