diff --git a/winsz.c b/winsz.c
index 19d66fb..e57c63b 100644
--- a/winsz.c
+++ b/winsz.c
@@ -5,6 +5,10 @@
 int main(void) {
     struct winsize w;
 
+    /* See: man 2 ioctl */
+    /* See: man 2 TIOCGWINSZ */
+    /* See: linux/fs/ioctl.c */
+    /* See: linux/drivers/tty/tty_io.c (L: ~2709 and ~2359) */
     if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &w) == -1) {
         perror("ioctl");
         return 1;