diff --git a/payload_consumer/payload_constants.h b/payload_consumer/payload_constants.h
index 9d29afd..ac3e882 100644
--- a/payload_consumer/payload_constants.h
+++ b/payload_consumer/payload_constants.h
@@ -49,6 +49,9 @@
 // The minor version that allows PUFFDIFF operation.
 extern const uint32_t kPuffdiffMinorPayloadVersion;
 
+// The maximum size of the payload header (anything before the protobuf).
+extern const uint64_t kMaxPayloadHeaderSize;
+
 // 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.