diff --git a/delta_performer.h b/delta_performer.h
index a57788d..b36c6ec 100644
--- a/delta_performer.h
+++ b/delta_performer.h
@@ -30,6 +30,9 @@
 // The minor version used by the A to B delta generator algorithm.
 extern const uint32_t kSourceMinorPayloadVersion;
 
+// Chunk size used for payloads during test.
+extern const size_t kDefaultChunkSize;
+
 class PrefsInterface;
 
 // This class performs the actions in a delta update synchronously. The delta