diff --git a/src/FieldNames.cpp b/src/FieldNames.cpp
index 66fc525585..7872f87c2e 100644
--- a/src/FieldNames.cpp
+++ b/src/FieldNames.cpp
@@ -14,9 +14,10 @@ std::map<int, SField::ptr> SField::codeToField;
 boost::mutex SField::mapMutex;
 
 SField sfInvalid(-1), sfGeneric(0);
-SField sfLedgerEntry(FIELD_CODE(STI_LEDGERENTRY, 1), STI_LEDGERENTRY, 1, "LedgerEntry");
-SField sfTransaction(FIELD_CODE(STI_TRANSACTION, 1), STI_TRANSACTION, 1, "Transaction");
-SField sfValidation(FIELD_CODE(STI_VALIDATION, 1), STI_VALIDATION, 1, "Validation");
+SField sfLedgerEntry(STI_LEDGERENTRY, 1, "LedgerEntry");
+SField sfTransaction(STI_TRANSACTION, 1, "Transaction");
+SField sfValidation(STI_VALIDATION, 1, "Validation");
+SField sfID(STI_HASH256, 257, "id");
 
 #define FIELD(name, type, index) SField sf##name(FIELD_CODE(STI_##type, index), STI_##type, index, #name);
 #define TYPE(name, type, index)
@@ -97,3 +98,13 @@ SField::ref SField::getField(const std::string& fieldName)
 	}
 	return sfInvalid;
 }
+
+SField::~SField()
+{
+	boost::mutex::scoped_lock sl(mapMutex);
+	std::map<int, ptr>::iterator it = codeToField.find(fieldCode);
+	if ((it != codeToField.end()) && (it->second == this))
+		codeToField.erase(it);
+}
+
+// vim:ts=4
diff --git a/src/FieldNames.h b/src/FieldNames.h
index 443ae50086..3316ae492d 100644
--- a/src/FieldNames.h
+++ b/src/FieldNames.h
@@ -54,12 +54,14 @@ public:
 		fieldCode(fc), fieldType(tid), fieldValue(fv), fieldName(fn)
 	{ codeToField[fieldCode] = this; }
 
-	SField(SerializedTypeID tid, int fv, const char *fn, bool temporary) :
+	SField(SerializedTypeID tid, int fv, const char *fn) :
 		fieldCode(FIELD_CODE(tid, fv)), fieldType(tid), fieldValue(fv), fieldName(fn)
-	{ if (!temporary) codeToField[fieldCode] = this; }
+	{ codeToField[fieldCode] = this; }
 
 	SField(int fc) : fieldCode(fc), fieldType(STI_UNKNOWN), fieldValue(0) { ; }
 
+	~SField();
+
 	static SField::ref getField(int fieldCode);
 	static SField::ref getField(int fieldType, int fieldValue);
 	static SField::ref getField(const std::string& fieldName);
@@ -71,6 +73,7 @@ public:
 	bool isGeneric() const		{ return fieldCode == 0; }
 	bool isInvalid() const		{ return fieldCode == -1; }
 	bool isKnown() const		{ return fieldType != STI_UNKNOWN; }
+	bool isBinary() const		{ return fieldValue < 256; }
 
 	bool operator==(const SField& f) const { return fieldCode == f.fieldCode; }
 	bool operator!=(const SField& f) const { return fieldCode != f.fieldCode; }