diff --git a/libc/include/strings.h b/libc/include/strings.h
index c2e0a5e..ccdac04 100644
--- a/libc/include/strings.h
+++ b/libc/include/strings.h
@@ -36,8 +36,12 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef _STRINGS_H_
-#define _STRINGS_H_
+#pragma once
+
+/**
+ * @file strings.h
+ * @brief Extra string functions.
+ */
 
 #include <sys/types.h>
 #include <sys/cdefs.h>
@@ -46,20 +50,28 @@
 #include <bits/strcasecmp.h>
 
 __BEGIN_DECLS
+
 #if defined(__BIONIC_FORTIFY)
+/** Deprecated. Use memmove() instead. */
 #define bcopy(b1, b2, len) (void)(__builtin___memmove_chk((b2), (b1), (len), __bos0(b2)))
+/** Deprecated. Use memset() instead. */
 #define bzero(b, len) (void)(__builtin___memset_chk((b), '\0', (len), __bos0(b)))
 #else
+/** Deprecated. Use memmove() instead. */
 #define bcopy(b1, b2, len) (void)(__builtin_memmove((b2), (b1), (len)))
+/** Deprecated. Use memset() instead. */
 #define bzero(b, len) (void)(__builtin_memset((b), '\0', (len)))
 #endif
 
 #if !defined(__i386__) || __ANDROID_API__ >= __ANDROID_API_J_MR2__
+/**
+ * [ffs(3)](http://man7.org/linux/man-pages/man3/ffs.3.html) finds the first set bit in `__i`.
+ *
+ * Returns 0 if no bit is set, or the index of the lowest set bit (counting from 1) otherwise.
+ */
 int ffs(int __i) __INTRODUCED_IN_X86(18);
 #endif
 
 __END_DECLS
 
 #include <android/legacy_strings_inlines.h>
-
-#endif