diff --git a/lladd/constants.h b/lladd/constants.h
index c7f4526..1eb878f 100644
--- a/lladd/constants.h
+++ b/lladd/constants.h
@@ -182,12 +182,15 @@ extern const short SLOT_TYPE_LENGTHS[];
 /*
   Definitions for different types of logs
 */
+/* A log type reservered for the log implementation.  Its format
+   depends on the physical log's implementation.  Most other code
+   (recovery, abort) should be prepared to accept and ignore these
+   entries. */
+#define INTERNALLOG 0
 #define UPDATELOG 1
 #define XBEGIN 2
 #define XCOMMIT 3
 #define XABORT 4
-/* Folded into update log entries */
-/*#define XALLOC 5*/
 /** 
     XEND is used for after the pages touched by a transaction have
     been flushed to stable storage.