diff --git a/src/ox/mc/presencemask.cpp b/src/ox/mc/presencemask.cpp
index 0860efdb7..2ae87bb34 100644
--- a/src/ox/mc/presencemask.cpp
+++ b/src/ox/mc/presencemask.cpp
@@ -10,9 +10,6 @@
 #include "err.hpp"
 #include "presencemask.hpp"
 
-#include <iostream>
-using namespace std;
-
 namespace ox {
 
 FieldPresenseMask::FieldPresenseMask(uint8_t *mask, size_t maxLen) {
@@ -45,4 +42,8 @@ void FieldPresenseMask::setMaxLen(int maxLen) {
 	m_maxLen = maxLen;
 }
 
+int FieldPresenseMask::getMaxLen() {
+	return m_maxLen;
+}
+
 }
diff --git a/src/ox/mc/presencemask.hpp b/src/ox/mc/presencemask.hpp
index 0001c1d29..13da66c3c 100644
--- a/src/ox/mc/presencemask.hpp
+++ b/src/ox/mc/presencemask.hpp
@@ -25,6 +25,8 @@ class FieldPresenseMask {
 		int set(int i, bool on);
 
 		void setMaxLen(int);
+
+		int getMaxLen();
 };
 
 }
diff --git a/src/ox/mc/read.hpp b/src/ox/mc/read.hpp
index 7ed0e7baa..e718ae423 100644
--- a/src/ox/mc/read.hpp
+++ b/src/ox/mc/read.hpp
@@ -57,9 +57,11 @@ class MetalClawReader {
 template<typename T>
 int MetalClawReader::op(const char*, T *val) {
 	int err = 0;
-	MetalClawReader reader(m_buff + m_buffIt, m_buffLen - m_buffIt);
-	err |= ioOp(&reader, val);
-	m_buffIt += reader.m_buffIt;
+	if (m_fieldPresence.get(m_field)) {
+		MetalClawReader reader(m_buff + m_buffIt, m_buffLen - m_buffIt);
+		err |= ioOp(&reader, val);
+		m_buffIt += reader.m_buffIt;
+	}
 	m_field++;
 	return err;
 };
diff --git a/src/ox/mc/write.hpp b/src/ox/mc/write.hpp
index c3b5b9f42..a68a994e7 100644
--- a/src/ox/mc/write.hpp
+++ b/src/ox/mc/write.hpp
@@ -81,9 +81,14 @@ int MetalClawWriter::op(const char*, ox::bstring<L> *val) {
 template<typename T>
 int MetalClawWriter::op(const char*, T *val) {
 	int err = 0;
+	bool fieldSet = false;
 	MetalClawWriter writer(m_buff + m_buffIt, m_buffLen - m_buffIt);
 	err |= ioOp(&writer, val);
-	m_buffIt += writer.m_buffIt;
+	if ((size_t) writer.m_fieldPresence.getMaxLen() < writer.m_buffIt) {
+		m_buffIt += writer.m_buffIt;
+		fieldSet = true;
+	}
+	err |= m_fieldPresence.set(m_field, fieldSet);
 	m_field++;
 	return err;
 };