diff --git a/README.md b/README.md
index 19ef96fae01..04816762f14 100644
--- a/README.md
+++ b/README.md
@@ -38,6 +38,7 @@ Read ["Installation"] from [The Book].
 3. Build and install:
 
     ```sh
+    $ git submodule update --init --recursive --progress
     $ ./x.py build && sudo ./x.py install
     ```