diff --git a/libc/include/syscall.h b/libc/include/syscall.h
index 4c30578..11d9655 100644
--- a/libc/include/syscall.h
+++ b/libc/include/syscall.h
@@ -1 +1,10 @@
+#pragma once
+
+/**
+ * @file syscall.h
+ * @brief Historical alternative to `<sys/syscall.h>`.
+ *
+ * New code should use `<sys/syscall.h>` directly.
+ */
+
 #include <sys/syscall.h>