diff --git a/include/linux/dax.h b/include/linux/dax.h
index 72dc81d..70600b6 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -5,6 +5,9 @@
 #include <linux/mm.h>
 #include <asm/pgtable.h>
 
+/* We use lowest available exceptional entry bit for locking */
+#define RADIX_DAX_ENTRY_LOCK (1 << RADIX_TREE_EXCEPTIONAL_SHIFT)
+
 ssize_t dax_do_io(struct kiocb *, struct inode *, struct iov_iter *, loff_t,
 		  get_block_t, dio_iodone_t, int flags);
 int dax_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);