diff --git a/block.h b/block.h
index ea12f5d..4e99e18 100644
--- a/block.h
+++ b/block.h
@@ -15,6 +15,7 @@
     int cluster_size;
     /* offset at which the VM state can be saved (0 if not possible) */
     int64_t vm_state_offset;
+    bool is_dirty;
 } BlockDriverInfo;
 
 typedef struct BlockFragInfo {