diff --git a/libevm/VM.h b/libevm/VM.h
index 7c1e66ed5..a1cb3eccb 100644
--- a/libevm/VM.h
+++ b/libevm/VM.h
@@ -188,6 +188,10 @@ template <class Ext> dev::bytesConstRef dev::eth::VM::go(Ext& _ext, OnOpFunc con
 		// EXECUTE...
 		switch (inst)
 		{
+		default:
+			BOOST_THROW_EXCEPTION(BadInstruction());
+			break;
+
 		case Instruction::ADD:
 			//pops two items and pushes S[-1] + S[-2] mod 2^256.
 			require(2);