diff --git a/Base/usr/share/man/man3/isatty.md b/Base/usr/share/man/man3/isatty.md
index 366607dcf1..f615d721b9 100644
--- a/Base/usr/share/man/man3/isatty.md
+++ b/Base/usr/share/man/man3/isatty.md
@@ -22,3 +22,4 @@ If `fd` refers to a TTY device, returns 1. Otherwise, returns 0 and `errno` is s
 
 * `EBADF`: `fd` is not an open file descriptor.
 * `ENOTTY`: `fd` refers to something that's not a TTY device.
+* `EINVAL`: `fd` refers to something that supports `ioctl()`, but is still not a TTY device.