diff --git a/firmware/application/capture_thread.hpp b/firmware/application/capture_thread.hpp
index 849a3131..6e2bbaa8 100644
--- a/firmware/application/capture_thread.hpp
+++ b/firmware/application/capture_thread.hpp
@@ -35,7 +35,7 @@
 
 class Writer {
 public:
-	virtual File::Result<size_t> write(const void* const buffer, const size_t bytes) = 0;
+	virtual File::Result<File::Size> write(const void* const buffer, const File::Size bytes) = 0;
 	virtual ~Writer() = default;
 };
 
diff --git a/firmware/application/file.cpp b/firmware/application/file.cpp
index 4ceb51aa..8c45c8b3 100644
--- a/firmware/application/file.cpp
+++ b/firmware/application/file.cpp
@@ -64,7 +64,7 @@ File::~File() {
 	f_close(&f);
 }
 
-File::Result<size_t> File::read(void* const data, const size_t bytes_to_read) {
+File::Result<File::Size> File::read(void* const data, const Size bytes_to_read) {
 	UINT bytes_read = 0;
 	const auto result = f_read(&f, data, bytes_to_read, &bytes_read);
 	if( result == FR_OK ) {
@@ -74,12 +74,12 @@ File::Result<size_t> File::read(void* const data, const size_t bytes_to_read) {
 	}
 }
 
-File::Result<size_t> File::write(const void* const data, const size_t bytes_to_write) {
+File::Result<File::Size> File::write(const void* const data, const Size bytes_to_write) {
 	UINT bytes_written = 0;
 	const auto result = f_write(&f, data, bytes_to_write, &bytes_written);
 	if( result == FR_OK ) {
 		if( bytes_to_write == bytes_written ) {
-			return { static_cast<size_t>(bytes_written) };
+			return { static_cast<File::Size>(bytes_written) };
 		} else {
 			return Error { FR_DISK_FULL };
 		}
@@ -88,7 +88,7 @@ File::Result<size_t> File::write(const void* const data, const size_t bytes_to_w
 	}
 }
 
-File::Result<uint64_t> File::seek(const uint64_t new_position) {
+File::Result<File::Offset> File::seek(const Offset new_position) {
 	/* NOTE: Returns *old* position, not new position */
 	const auto old_position = f_tell(&f);
 	const auto result = f_lseek(&f, new_position);
@@ -98,7 +98,7 @@ File::Result<uint64_t> File::seek(const uint64_t new_position) {
 	if( f_tell(&f) != new_position ) {
 		return { static_cast<Error>(FR_BAD_SEEK) };
 	}
-	return { static_cast<uint64_t>(old_position) };
+	return { static_cast<File::Offset>(old_position) };
 }
 
 Optional<File::Error> File::write_line(const std::string& s) {
diff --git a/firmware/application/file.hpp b/firmware/application/file.hpp
index 62813e21..64691703 100644
--- a/firmware/application/file.hpp
+++ b/firmware/application/file.hpp
@@ -136,6 +136,8 @@ std::filesystem::path next_filename_stem_matching_pattern(const std::filesystem:
 
 class File {
 public:
+	using Size = uint64_t;
+	using Offset = uint64_t;
 	using Error = std::filesystem::filesystem_error;
 
 	template<typename T>
@@ -200,13 +202,13 @@ public:
 	Optional<Error> append(const std::filesystem::path& filename);
 	Optional<Error> create(const std::filesystem::path& filename);
 
-	Result<size_t> read(void* const data, const size_t bytes_to_read);
-	Result<size_t> write(const void* const data, const size_t bytes_to_write);
+	Result<Size> read(void* const data, const Size bytes_to_read);
+	Result<Size> write(const void* const data, const Size bytes_to_write);
 
-	Result<uint64_t> seek(const uint64_t new_position);
+	Result<Offset> seek(const uint64_t Offset);
 
 	template<size_t N>
-	Result<size_t> write(const std::array<uint8_t, N>& data) {
+	Result<Size> write(const std::array<uint8_t, N>& data) {
 		return write(data.data(), N);
 	}
 
diff --git a/firmware/application/ui_record_view.cpp b/firmware/application/ui_record_view.cpp
index 42e0d374..71211dfc 100644
--- a/firmware/application/ui_record_view.cpp
+++ b/firmware/application/ui_record_view.cpp
@@ -48,7 +48,7 @@ public:
 		return file.create(filename);
 	}
 
-	File::Result<size_t> write(const void* const buffer, const size_t bytes) override {
+	File::Result<File::Size> write(const void* const buffer, const File::Size bytes) override {
 		auto write_result = file.write(buffer, bytes) ;
 		if( write_result.is_ok() ) {
 			bytes_written += write_result.value();
diff --git a/firmware/application/ui_sd_card_debug.cpp b/firmware/application/ui_sd_card_debug.cpp
index dd92f5c6..856f3e63 100644
--- a/firmware/application/ui_sd_card_debug.cpp
+++ b/firmware/application/ui_sd_card_debug.cpp
@@ -51,13 +51,13 @@ public:
 		halrtcnt_t write_duration_min { 0 };
 		halrtcnt_t write_duration_max { 0 };
 		halrtcnt_t write_test_duration { 0 };
-		size_t write_bytes { 0 };
+		File::Size write_bytes { 0 };
 		size_t write_count { 0 };
 
 		halrtcnt_t read_duration_min { 0 };
 		halrtcnt_t read_duration_max { 0 };
 		halrtcnt_t read_test_duration { 0 };
-		size_t read_bytes { 0 };
+		File::Size read_bytes { 0 };
 		size_t read_count { 0 };
 	};
 
@@ -80,9 +80,9 @@ public:
 	}
 
 private:
-	static constexpr size_t write_size = 16384;
-	static constexpr size_t bytes_to_write = 16 * 1024 * 1024;
-	static constexpr size_t bytes_to_read = bytes_to_write;
+	static constexpr File::Size write_size = 16384;
+	static constexpr File::Size bytes_to_write = 16 * 1024 * 1024;
+	static constexpr File::Size bytes_to_read = bytes_to_write;
 
 	static Thread* thread;
 	volatile Result _result { Result::Incomplete };
@@ -365,7 +365,7 @@ static std::string format_ticks_as_ms(const halrtcnt_t value) {
 	return format_3dot3_string(us);
 }
 
-static std::string format_bytes_per_ticks_as_mib(const size_t bytes, const halrtcnt_t ticks) {
+static std::string format_bytes_per_ticks_as_mib(const File::Size bytes, const halrtcnt_t ticks) {
 	const uint32_t bps = uint64_t(bytes) * halGetCounterFrequency() / ticks;
 	const uint32_t kbps = bps / 1000U;
 	return format_3dot3_string(kbps);