diff --git a/README.md b/README.md
index c4953379..dba4fa69 100644
--- a/README.md
+++ b/README.md
@@ -36,7 +36,7 @@ This repository contains the source code for the _Writing an OS in Rust_ series
 - [Set Up GDB](http://os.phil-opp.com/set-up-gdb.html)
 
 ## Building
-You need to have `nasm`, `grub-mkrescue`, `xorriso`, `qemu` and a nighly Rust compiler installed. Then you can run it using `make run`.
+You need to have `nasm`, `grub-mkrescue`, `mformat` (included in `mtools`), `xorriso`, `qemu` and a nighly Rust compiler installed. Then you can run it using `make run`.
 
 Please file an issue if you run into any problems.