diff --git a/docs/proposals/20190610-machine-states-preboot-bootstrapping.md b/docs/proposals/20190610-machine-states-preboot-bootstrapping.md
index 8748352cc548..0604dbe5ad11 100644
--- a/docs/proposals/20190610-machine-states-preboot-bootstrapping.md
+++ b/docs/proposals/20190610-machine-states-preboot-bootstrapping.md
@@ -116,6 +116,7 @@ In Cluster API v1alpha1, users can create Machine custom resources. When a Machi
 1. To setup OS configuration, install software or any other features related to image building.
 1. To support post-boot configuration of Machine.
 1. To revisit MachineClass role and functionality.
+1. To customize the image beyond the settings required to run kubelet, that is an implementation constraint of the bootstrap provider.
 
 ## Proposal
 In this section we outline the proposed API changes; describe states, transitions, and sequence diagrams for the most important scenarios; and provide a kubeadm-based example.