diff --git a/libethcore/ICAP.cpp b/libethcore/ICAP.cpp
index 107d79db1..d4c4f9c46 100644
--- a/libethcore/ICAP.cpp
+++ b/libethcore/ICAP.cpp
@@ -141,15 +141,13 @@ Address ICAP::lookup(std::function<bytes(Address, bytes)> const& _call, Address
 	if (m_asset == "XET")
 	{
 		// TODO
-//		_call(_reg, );
-		return Address();
+		throw InterfaceNotSupported("ICAP::lookup(), XET asset");
 	}
 	else if (m_asset == "ETH")
 	{
 		// TODO
-
 //		return resolve(m_institution + "/" + m_client).primary();
-		return Address();
+		throw InterfaceNotSupported("ICAP::lookup(), ETH asset");
 	}
 	else
 		throw InterfaceNotSupported("ICAP::lookup(), non XET asset");
diff --git a/libethcore/ICAP.h b/libethcore/ICAP.h
index 7d5ce1f51..fd5db2f0a 100644
--- a/libethcore/ICAP.h
+++ b/libethcore/ICAP.h
@@ -39,6 +39,10 @@ struct InvalidICAP: virtual public dev::Exception {};
 
 static const std::string EmptyString;
 
+/**
+ * @brief Encapsulation of an ICAP address.
+ * Can be encoded, decoded, looked-up and inspected.
+ */
 class ICAP
 {
 public:
@@ -74,7 +78,7 @@ public:
 	/// @returns type of ICAP.
 	Type type() const { return m_type; }
 	/// @returns target address. Only valid when type() == Direct.
-	Address const& direct() const { return m_type == Direct ? m_direct : Address(); }
+	Address const& direct() const { return m_type == Direct ? m_direct : ZeroAddress; }
 	/// @returns asset. Only valid when type() == Indirect.
 	std::string const& asset() const { return m_type == Indirect ? m_asset : EmptyString; }
 	/// @returns target name. Only valid when type() == Indirect and asset() == "ETH".
diff --git a/libethereum/Transaction.cpp b/libethereum/Transaction.cpp
index 411c8bd99..975af53a5 100644
--- a/libethereum/Transaction.cpp
+++ b/libethereum/Transaction.cpp
@@ -105,7 +105,7 @@ Address const& Transaction::safeSender() const noexcept
 	catch (...)
 	{
 		cwarn << "safeSender() did throw an exception: " <<  boost::current_exception_diagnostic_information();
-		return NullAddress;
+		return ZeroAddress;
 	}
 }
 
diff --git a/libethereum/Transaction.h b/libethereum/Transaction.h
index faf5ea07a..0ce536b78 100644
--- a/libethereum/Transaction.h
+++ b/libethereum/Transaction.h
@@ -97,8 +97,6 @@ struct ExecutionResult
 
 std::ostream& operator<<(std::ostream& _out, ExecutionResult const& _er);
 
-static const Address NullAddress;
-
 /// Encodes a transaction, ready to be exported to or freshly imported from RLP.
 class Transaction
 {