diff --git a/libc/include/sys/sysmacros.h b/libc/include/sys/sysmacros.h
index 592cc5e..64cf289 100644
--- a/libc/include/sys/sysmacros.h
+++ b/libc/include/sys/sysmacros.h
@@ -26,21 +26,26 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _SYS_SYSMACROS_H_
-#define _SYS_SYSMACROS_H_
+#pragma once
+
+/**
+ * @file sys/sysmacros.h
+ * @brief Major/minor device number macros.
+ */
 
 #include <sys/cdefs.h>
 
+/** Combines `major` and `minor` into a device number. */
 #define makedev(__major, __minor) \
   ( \
     (((__major) & 0xfffff000ULL) << 32) | (((__major) & 0xfffULL) << 8) | \
     (((__minor) & 0xffffff00ULL) << 12) | (((__minor) & 0xffULL)) \
   )
 
+/** Extracts the major part of a device number. */
 #define major(__dev) \
   ((unsigned) ((((unsigned long long) (__dev) >> 32) & 0xfffff000) | (((__dev) >> 8) & 0xfff)))
 
+/** Extracts the minor part of a device number. */
 #define minor(__dev) \
   ((unsigned) ((((__dev) >> 12) & 0xffffff00) | ((__dev) & 0xff)))
-
-#endif /* _SYS_SYSMACROS_H_ */