diff --git a/libc/include/sys/signalfd.h b/libc/include/sys/signalfd.h
index 2337cd7..bd911f7 100644
--- a/libc/include/sys/signalfd.h
+++ b/libc/include/sys/signalfd.h
@@ -26,8 +26,12 @@
  * SUCH DAMAGE.
  */
 
-#ifndef _SYS_SIGNALFD_H_
-#define _SYS_SIGNALFD_H_
+#pragma once
+
+/**
+ * @file sys/signalfd.h
+ * @brief File-descriptor based signal interface.
+ */
 
 #include <sys/cdefs.h>
 
@@ -36,9 +40,19 @@
 
 __BEGIN_DECLS
 
+/**
+ * [signalfd(2)](http://man7.org/linux/man-pages/man2/signalfd.2.html) creates/manipulates a
+ * file descriptor for reading signal events.
+ *
+ * Returns the file descriptor on success, and returns -1 and sets `errno` on failure.
+ *
+ * Available since API level 18.
+ */
 int signalfd(int __fd, const sigset_t* __mask, int __flags) __INTRODUCED_IN(18);
+
+/**
+ * Like signalfd() but allows setting a signal mask with RT signals even from a 32-bit process.
+ */
 int signalfd64(int __fd, const sigset64_t* __mask, int __flags) __INTRODUCED_IN(28);
 
 __END_DECLS
-
-#endif