diff --git a/libc/include/sys/limits.h b/libc/include/sys/limits.h
index 1e189a1..33ccaee 100644
--- a/libc/include/sys/limits.h
+++ b/libc/include/sys/limits.h
@@ -1 +1,10 @@
+#pragma once
+
+/**
+ * @file sys/limits.h
+ * @brief Historical synonym for `<limits.h>`.
+ *
+ * New code should use `<limits.h>` directly.
+ */
+
 #include <limits.h>