diff --git a/install_plan.h b/install_plan.h
index 6e6f7ae..5e50626 100644
--- a/install_plan.h
+++ b/install_plan.h
@@ -31,6 +31,9 @@
 // parts of the update system about the install that should happen.
 namespace chromeos_update_engine {
 
+// The kernel and rootfs partition names used by the BootControlInterface when
+// handling update payloads with a major version 1. The names of the updated
+// partitions are include in the payload itself for major version 2.
 // TODO(deymo): Remove these constants from this interface once the InstallPlan
 // doesn't list the partitions explicitly.
 extern const char* kLegacyPartitionNameKernel;