diff --git a/libc/include/endian.h b/libc/include/endian.h
index 65e2930..ed237b9 100644
--- a/libc/include/endian.h
+++ b/libc/include/endian.h
@@ -1 +1,10 @@
+#pragma once
+
+/*
+ * @file endian.h
+ * @brief Historical alternative to `<sys/endian.h>`.
+ *
+ * New code should use `<sys/endian.h>` directly.
+ */
+
 #include <sys/endian.h>