diff --git a/libc/include/sys/poll.h b/libc/include/sys/poll.h
index 779ec77..0323e37 100644
--- a/libc/include/sys/poll.h
+++ b/libc/include/sys/poll.h
@@ -1 +1,10 @@
+#pragma once
+
+/**
+ * @file sys/poll.h
+ * @brief Historical synonym for `<poll.h>`.
+ *
+ * New code should use `<poll.h>` directly.
+ */
+
 #include <poll.h>