diff --git a/libevm/VM.h b/libevm/VM.h
index ce8001bbf..eed1988bb 100644
--- a/libevm/VM.h
+++ b/libevm/VM.h
@@ -261,6 +261,7 @@ template <class Ext> dev::bytesConstRef dev::eth::VM::go(Ext& _ext, OnOpFunc con
 		case Instruction::OR:
 		case Instruction::XOR:
 		case Instruction::BYTE:
+		case Instruction::SIGNEXTEND:
 		case Instruction::JUMPI:
 			require(2);
 			break;
@@ -420,6 +421,19 @@ template <class Ext> dev::bytesConstRef dev::eth::VM::go(Ext& _ext, OnOpFunc con
 			m_stack.pop_back();
 			m_stack.pop_back();
 			break;
+		case Instruction::SIGNEXTEND:
+			if (m_stack.back() < 31)
+			{
+				unsigned const testBit(m_stack.back() * 8 + 7);
+				u256& number = m_stack[m_stack.size() - 2];
+				u256 mask = ((u256(1) << testBit) - 1);
+				if (boost::multiprecision::bit_test(number, testBit))
+					number |= ~mask;
+				else
+					number &= mask;
+			}
+			m_stack.pop_back();
+			break;
 		case Instruction::SHA3:
 		{
 			unsigned inOff = (unsigned)m_stack.back();
diff --git a/libevmface/Instruction.cpp b/libevmface/Instruction.cpp
index 7b253f388..238b21512 100644
--- a/libevmface/Instruction.cpp
+++ b/libevmface/Instruction.cpp
@@ -52,6 +52,7 @@ const std::map<std::string, Instruction> dev::eth::c_instructions =
 	{ "BYTE", Instruction::BYTE },
 	{ "ADDMOD", Instruction::ADDMOD },
 	{ "MULMOD", Instruction::MULMOD },
+	{ "SIGNEXTEND", Instruction::SIGNEXTEND },
 	{ "SHA3", Instruction::SHA3 },
 	{ "ADDRESS", Instruction::ADDRESS },
 	{ "BALANCE", Instruction::BALANCE },
@@ -179,6 +180,7 @@ static const std::map<Instruction, InstructionInfo> c_instructionInfo =
 	{ Instruction::BYTE,		{ "BYTE",			0, 2, 1 } },
 	{ Instruction::ADDMOD,		{ "ADDMOD",			0, 3, 1 } },
 	{ Instruction::MULMOD,		{ "MULMOD",			0, 3, 1 } },
+	{ Instruction::SIGNEXTEND,	{ "SIGNEXTEND",		0, 2, 1 } },
 	{ Instruction::SHA3,		{ "SHA3",			0, 2, 1 } },
 	{ Instruction::ADDRESS,		{ "ADDRESS",		0, 0, 1 } },
 	{ Instruction::BALANCE,		{ "BALANCE",		0, 1, 1 } },
diff --git a/libevmface/Instruction.h b/libevmface/Instruction.h
index b6aa477b1..ce587dfaf 100644
--- a/libevmface/Instruction.h
+++ b/libevmface/Instruction.h
@@ -58,6 +58,7 @@ enum class Instruction: uint8_t
 	BYTE,				///< retrieve single byte from word
 	ADDMOD,				///< unsigned modular addition
 	MULMOD,				///< unsigned modular multiplication
+	SIGNEXTEND,			///< perform sign extension starting at given bit
 	SHA3 = 0x20,		///< compute SHA3-256 hash
 
 	ADDRESS = 0x30,		///< get address of currently executing account
diff --git a/libserpent/opcodes.h b/libserpent/opcodes.h
index 552364731..f02a5aa6d 100644
--- a/libserpent/opcodes.h
+++ b/libserpent/opcodes.h
@@ -42,8 +42,9 @@ Mapping mapping[] = {
     Mapping("XOR", 0x12, 2, 1),
     Mapping("BYTE", 0x13, 2, 1),
     Mapping("ADDMOD", 0x14, 3, 1),
-    Mapping("MULMOD", 0x15, 3, 1),
-    Mapping("SHA3", 0x20, 2, 1),
+	Mapping("MULMOD", 0x15, 3, 1),
+	Mapping("SIGNEXTEND", 0x16, 2, 1),
+	Mapping("SHA3", 0x20, 2, 1),
     Mapping("ADDRESS", 0x30, 0, 1),
     Mapping("BALANCE", 0x31, 1, 1),
     Mapping("ORIGIN", 0x32, 0, 1),