diff --git a/include/exec/memory.h b/include/exec/memory.h
index b8e76f44b3..d5e9d58102 100644
--- a/include/exec/memory.h
+++ b/include/exec/memory.h
@@ -35,7 +35,8 @@ typedef struct MemoryRegionMmio MemoryRegionMmio;
 
 #define DIRTY_MEMORY_VGA       0
 #define DIRTY_MEMORY_CODE      1
-#define DIRTY_MEMORY_MIGRATION 3
+#define DIRTY_MEMORY_MIGRATION 2
+#define DIRTY_MEMORY_NUM       3        /* num of dirty bits */
 
 struct MemoryRegionMmio {
     CPUReadMemoryFunc *read[3];