diff --git a/libc/include/sys/errno.h b/libc/include/sys/errno.h
index 339f4fc..77526a9 100644
--- a/libc/include/sys/errno.h
+++ b/libc/include/sys/errno.h
@@ -1 +1,10 @@
+#pragma once
+
+/**
+ * @file sys/errno.h
+ * @brief Historical synonym for `<errno.h>`.
+ *
+ * New code should use `<errno.h>` directly.
+ */
+
 #include <errno.h>
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>
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>
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>
diff --git a/libc/include/sys/signal.h b/libc/include/sys/signal.h
index 2e602da..fde0819 100644
--- a/libc/include/sys/signal.h
+++ b/libc/include/sys/signal.h
@@ -1 +1,10 @@
+#pragma once
+
+/**
+ * @file sys/signal.h
+ * @brief Historical synonym for `<signal.h>`.
+ *
+ * New code should use `<signal.h>` directly.
+ */
+
 #include <signal.h>
diff --git a/libc/include/sys/sysconf.h b/libc/include/sys/sysconf.h
index eb30faf..060ba7e 100644
--- a/libc/include/sys/sysconf.h
+++ b/libc/include/sys/sysconf.h
@@ -1,6 +1,14 @@
-/*
+#pragma once
+
+/**
+ * @file sys/sysconf.h
+ * @brief Historical synonym for `<sysconf.h>`.
+ *
  * This file used to contain the declarations of sysconf and its associated constants.
- * No standard mentions a <sys/sysconf.h>, but there are enough users in vendor (and potential ones
- * in the NDK) to warrant not breaking source compatibility.
+ * No standard mentions a `<sys/sysconf.h>`, but there are enough users in vendor (and
+ * potential NDK users) to warrant not breaking source compatibility.
+ *
+ * New code should use `<sysconf.h>` directly.
  */
+
 #include <bits/sysconf.h>
diff --git a/libc/include/sys/syslog.h b/libc/include/sys/syslog.h
index 7761ece..4b89c10 100644
--- a/libc/include/sys/syslog.h
+++ b/libc/include/sys/syslog.h
@@ -1 +1,10 @@
+#pragma once
+
+/**
+ * @file sys/syslog.h
+ * @brief Historical synonym for `<syslog.h>`.
+ *
+ * New code should use `<syslog.h>` directly.
+ */
+
 #include <syslog.h>
diff --git a/libc/include/sys/unistd.h b/libc/include/sys/unistd.h
index 1e823fb..eb7694d 100644
--- a/libc/include/sys/unistd.h
+++ b/libc/include/sys/unistd.h
@@ -1 +1,10 @@
+#pragma once
+
+/**
+ * @file sys/unistd.h
+ * @brief Historical synonym for `<unistd.h>`.
+ *
+ * New code should use `<unistd.h>` directly.
+ */
+
 #include <unistd.h>