diff --git a/INSTALL.md b/INSTALL.md
index 52e67b4b..5914b794 100644
--- a/INSTALL.md
+++ b/INSTALL.md
@@ -112,6 +112,7 @@ Once you have `flatpak` and `flatpak-builder` installed:
 ```
 git clone git://github.com/Bitmessage/PyBitmessage.git
 cd PyBitmessage/
+git submodule add https://github.com/flathub/shared-modules.git
 flatpak-builder --install _flatpak -install-deps-from=flathub --force-clean --user org.bitmessage.PyBitmessage.json
 ```
 This will install PyBitmessage to your local flatpak user repository, but it