diff --git a/src/io/FileDescriptor.cxx b/src/io/FileDescriptor.cxx
index 08b457831..5d0dd17f2 100644
--- a/src/io/FileDescriptor.cxx
+++ b/src/io/FileDescriptor.cxx
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 Max Kellermann <max.kellermann@gmail.com>
+ * Copyright 2012-2020 Max Kellermann <max.kellermann@gmail.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -32,6 +32,7 @@
 
 #include <cassert>
 #include <cstdint>
+#include <stdexcept>
 
 #include <sys/stat.h>
 #include <fcntl.h>
@@ -289,7 +290,7 @@ FileDescriptor::GetSize() const noexcept
 }
 
 void
-FileDescriptor::FullRead(void *_buffer, size_t length)
+FileDescriptor::FullRead(void *_buffer, std::size_t length)
 {
 	auto buffer = (uint8_t *)_buffer;
 
@@ -307,7 +308,7 @@ FileDescriptor::FullRead(void *_buffer, size_t length)
 }
 
 void
-FileDescriptor::FullWrite(const void *_buffer, size_t length)
+FileDescriptor::FullWrite(const void *_buffer, std::size_t length)
 {
 	auto buffer = (const uint8_t *)_buffer;
 
diff --git a/src/io/FileDescriptor.hxx b/src/io/FileDescriptor.hxx
index 3b33081bf..c180bf7f4 100644
--- a/src/io/FileDescriptor.hxx
+++ b/src/io/FileDescriptor.hxx
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2019 Max Kellermann <max.kellermann@gmail.com>
+ * Copyright 2012-2020 Max Kellermann <max.kellermann@gmail.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -32,6 +32,7 @@
 
 #include "util/Compiler.h"
 
+#include <cstddef>
 #include <utility>
 
 #include <unistd.h>
@@ -229,7 +230,7 @@ public:
 	gcc_pure
 	off_t GetSize() const noexcept;
 
-	ssize_t Read(void *buffer, size_t length) noexcept {
+	ssize_t Read(void *buffer, std::size_t length) noexcept {
 		return ::read(fd, buffer, length);
 	}
 
@@ -237,9 +238,9 @@ public:
 	 * Read until all of the given buffer has been filled.  Throws
 	 * on error.
 	 */
-	void FullRead(void *buffer, size_t length);
+	void FullRead(void *buffer, std::size_t length);
 
-	ssize_t Write(const void *buffer, size_t length) noexcept {
+	ssize_t Write(const void *buffer, std::size_t length) noexcept {
 		return ::write(fd, buffer, length);
 	}