diff --git a/deps/ox/src/ox/mc/presenceindicator.cpp b/deps/ox/src/ox/mc/presenceindicator.cpp
index ba854a50..72a4e9a5 100644
--- a/deps/ox/src/ox/mc/presenceindicator.cpp
+++ b/deps/ox/src/ox/mc/presenceindicator.cpp
@@ -12,26 +12,18 @@
 
 namespace ox {
 
-FieldPresenceIndicator::FieldPresenceIndicator(const uint8_t *mask, std::size_t maxLen) {
-	// TODO: have separate read only version of this class
-	m_mask = const_cast<uint8_t*>(mask);
-	m_maskLen = maxLen;
+template class FieldBitmapReader<uint8_t*>;
+template class FieldBitmapReader<const uint8_t*>;
+
+FieldBitmap::FieldBitmap(uint8_t *mask, std::size_t maxLen) noexcept: FieldBitmapReader<uint8_t*>(mask, maxLen) {
 }
 
-Result<bool> FieldPresenceIndicator::get(std::size_t i) const {
-	if (i / 8 < m_maskLen) {
-		return (m_mask[i / 8] >> (i % 8)) & 1;
-	} else {
-		return OxError(MC_PRESENCEMASKOUTBOUNDS);
-	}
-}
-
-Error FieldPresenceIndicator::set(std::size_t i, bool on) {
-	if (i / 8 < m_maskLen) {
+Error FieldBitmap::set(std::size_t i, bool on) noexcept {
+	if (i / 8 < m_mapLen) {
 		if (on) {
-			m_mask[i / 8] |= 1 << (i % 8);
+			m_map[i / 8] |= 1 << (i % 8);
 		} else {
-			m_mask[i / 8] &= ~(1 << (i % 8));
+			m_map[i / 8] &= ~(1 << (i % 8));
 		}
 		return OxError(0);
 	} else {
@@ -39,17 +31,4 @@ Error FieldPresenceIndicator::set(std::size_t i, bool on) {
 	}
 }
 
-void FieldPresenceIndicator::setFields(int fields) noexcept {
-	m_fields = fields;
-	m_maskLen = (fields / 8 + 1) - (fields % 8 == 0);
-}
-
-	void FieldPresenceIndicator::setMaxLen(int maxLen) noexcept {
-	m_maskLen = maxLen;
-}
-
-int FieldPresenceIndicator::getMaxLen() const noexcept {
-	return m_maskLen;
-}
-
 }
diff --git a/deps/ox/src/ox/mc/presenceindicator.hpp b/deps/ox/src/ox/mc/presenceindicator.hpp
index 6cff766b..928a7f32 100644
--- a/deps/ox/src/ox/mc/presenceindicator.hpp
+++ b/deps/ox/src/ox/mc/presenceindicator.hpp
@@ -13,25 +13,67 @@
 
 namespace ox {
 
-class FieldPresenceIndicator {
-	private:
-		uint8_t *m_mask = nullptr;
-		std::size_t m_maskLen = 0;
+template<typename T>
+class FieldBitmapReader {
+	protected:
+		T m_map = nullptr;
+		std::size_t m_mapLen = 0;
 		std::size_t m_fields = 0;
 
 	public:
-		FieldPresenceIndicator(const uint8_t *mask, std::size_t maxLen);
+		FieldBitmapReader(T map, std::size_t maxLen) noexcept;
 
-		Result<bool> get(std::size_t i) const;
-
-		Error set(std::size_t i, bool on);
+		Result<bool> get(std::size_t i) const noexcept;
 
 		void setFields(int) noexcept;
 
-	void setMaxLen(int) noexcept;
+		void setMaxLen(int) noexcept;
 
 		int getMaxLen() const noexcept;
 
 };
 
+template<typename T>
+FieldBitmapReader<T>::FieldBitmapReader(T map, std::size_t maxLen) noexcept {
+	m_map = map;
+	m_mapLen = maxLen;
+}
+
+template<typename T>
+Result<bool> FieldBitmapReader<T>::get(std::size_t i) const noexcept {
+	if (i / 8 < m_mapLen) {
+		return (m_map[i / 8] >> (i % 8)) & 1;
+	} else {
+		return OxError(MC_PRESENCEMASKOUTBOUNDS);
+	}
+}
+
+template<typename T>
+void FieldBitmapReader<T>::setFields(int fields) noexcept {
+	m_fields = fields;
+	m_mapLen = (fields / 8 + 1) - (fields % 8 == 0);
+}
+
+template<typename T>
+void FieldBitmapReader<T>::setMaxLen(int maxLen) noexcept {
+	m_mapLen = maxLen;
+}
+
+template<typename T>
+int FieldBitmapReader<T>::getMaxLen() const noexcept {
+	return m_mapLen;
+}
+
+extern template class FieldBitmapReader<uint8_t*>;
+extern template class FieldBitmapReader<const uint8_t*>;
+
+class FieldBitmap: public FieldBitmapReader<uint8_t*> {
+
+	public:
+		FieldBitmap(uint8_t *mask, std::size_t maxLen) noexcept;
+
+		Error set(std::size_t i, bool on) noexcept;
+
+};
+
 }
diff --git a/deps/ox/src/ox/mc/read.hpp b/deps/ox/src/ox/mc/read.hpp
index 433d19c6..d4448aff 100644
--- a/deps/ox/src/ox/mc/read.hpp
+++ b/deps/ox/src/ox/mc/read.hpp
@@ -25,7 +25,7 @@ namespace ox {
 class MetalClawReader {
 
 	private:
-		FieldPresenceIndicator m_fieldPresence;
+		FieldBitmapReader<const uint8_t*> m_fieldPresence;
 		int m_fields = 0;
 		int m_field = 0;
 		int m_unionIdx = -1;
diff --git a/deps/ox/src/ox/mc/write.hpp b/deps/ox/src/ox/mc/write.hpp
index 8a08971e..c10c44d5 100644
--- a/deps/ox/src/ox/mc/write.hpp
+++ b/deps/ox/src/ox/mc/write.hpp
@@ -28,7 +28,7 @@ namespace ox {
 class MetalClawWriter {
 
 	private:
-		FieldPresenceIndicator m_fieldPresence;
+		FieldBitmap m_fieldPresence;
 		int m_fields = 0;
 		int m_field = 0;
 		int m_unionIdx = -1;