diff --git a/libc/include/sys/fcntl.h b/libc/include/sys/fcntl.h
index cd30455..35e677a 100644
--- a/libc/include/sys/fcntl.h
+++ b/libc/include/sys/fcntl.h
@@ -1 +1,10 @@
+#pragma once
+
+/**
+ * @file sys/fcntl.h
+ * @brief Historical synonym for `<fcntl.h>`.
+ *
+ * New code should use `<fcntl.h>` directly.
+ */
+
 #include <fcntl.h>