diff --git a/inc/MemoryMapping.h b/inc/MemoryMapping.h
index b702a72..6ccd3fa 100644
--- a/inc/MemoryMapping.h
+++ b/inc/MemoryMapping.h
@@ -11,6 +11,8 @@ namespace EightBit {
 
 		enum class AccessLevel { Unknown, ReadOnly, WriteOnly, ReadWrite };
 
+		constexpr auto offset(uint16_t address) const noexcept { return (address - begin) & mask; }
+
 		Memory& memory;
 		uint16_t begin = Chip::Mask16;
 		uint16_t mask = 0U;
diff --git a/src/Bus.cpp b/src/Bus.cpp
index 4cba73e..1924b79 100644
--- a/src/Bus.cpp
+++ b/src/Bus.cpp
@@ -40,10 +40,8 @@ void EightBit::Bus::loadHexFile(const std::string path) {
 
 uint8_t& EightBit::Bus::reference(const uint16_t address) noexcept {
 	const auto mapped = mapping(address);
-	const uint16_t offset = (address - mapped.begin) & mapped.mask;
-	if (mapped.access == MemoryMapping::AccessLevel::ReadOnly) {
-		DATA() = mapped.memory.peek(offset);
-		return DATA();
-	}
-	return mapped.memory.reference(offset);
+	const auto offset = mapped.offset(address);
+	if (mapped.access != MemoryMapping::AccessLevel::ReadOnly)
+		return mapped.memory.reference(offset);
+	return DATA() = mapped.memory.peek(offset);
 }