diff --git a/payload_constants.h b/payload_constants.h
index 55a82d3..188ea84 100644
--- a/payload_constants.h
+++ b/payload_constants.h
@@ -23,6 +23,12 @@
 
 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.
+extern const char kLegacyPartitionNameKernel[];
+extern const char kLegacyPartitionNameRoot[];
+
 extern const char kBspatchPath[];
 extern const char kDeltaMagic[];