diff --git a/src/structs.h b/src/structs.h
index 9e40928..a537ccb 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -756,10 +756,11 @@
     int		ml_stack_top;	// current top of ml_stack
     int		ml_stack_size;	// total number of entries in ml_stack
 
-#define ML_EMPTY	1	// empty buffer
-#define ML_LINE_DIRTY	2	// cached line was changed and allocated
-#define ML_LOCKED_DIRTY	4	// ml_locked was changed
-#define ML_LOCKED_POS	8	// ml_locked needs positive block number
+#define ML_EMPTY	0x01	// empty buffer
+#define ML_LINE_DIRTY	0x02	// cached line was changed and allocated
+#define ML_LOCKED_DIRTY	0x04	// ml_locked was changed
+#define ML_LOCKED_POS	0x08	// ml_locked needs positive block number
+#define ML_ALLOCATED	0x10	// ml_line_ptr is an allocated copy
     int		ml_flags;
 
     colnr_T	ml_line_len;	// length of the cached line, including NUL