diff --git a/build/docs/mozinfo.rst b/build/docs/mozinfo.rst
index 0d4b8e43148f..f3d0439aa5a3 100644
--- a/build/docs/mozinfo.rst
+++ b/build/docs/mozinfo.rst
@@ -59,6 +59,12 @@ bits
 
    Optional.
 
+buildapp
+   The path to the XUL application being built.
+
+   For desktop Firefox, this is ``browser``. For Fennec, it's
+   ``mobile/android``. For B2G, it's ``b2g``.
+
 crashreporter
    Whether the crash reporter is enabled for this build.