diff --git a/fs/ocfs2/ocfs2_fs.h b/fs/ocfs2/ocfs2_fs.h
index f0d9eb0..c20a74b 100644
--- a/fs/ocfs2/ocfs2_fs.h
+++ b/fs/ocfs2/ocfs2_fs.h
@@ -88,7 +88,7 @@
 #define OCFS2_FEATURE_COMPAT_SUPP	OCFS2_FEATURE_COMPAT_BACKUP_SB
 #define OCFS2_FEATURE_INCOMPAT_SUPP	(OCFS2_FEATURE_INCOMPAT_LOCAL_MOUNT \
 					 | OCFS2_FEATURE_INCOMPAT_SPARSE_ALLOC)
-#define OCFS2_FEATURE_RO_COMPAT_SUPP	0
+#define OCFS2_FEATURE_RO_COMPAT_SUPP	OCFS2_FEATURE_RO_COMPAT_UNWRITTEN
 
 /*
  * Heartbeat-only devices are missing journals and other files.  The
@@ -116,6 +116,11 @@
  */
 #define OCFS2_FEATURE_COMPAT_BACKUP_SB		0x0001
 
+/*
+ * Unwritten extents support.
+ */
+#define OCFS2_FEATURE_RO_COMPAT_UNWRITTEN	0x0001
+
 /* The byte offset of the first backup block will be 1G.
  * The following will be 4G, 16G, 64G, 256G and 1T.
  */