diff --git a/libxfs/xfs_format.h b/libxfs/xfs_format.h
index 2aea080..13f3687 100644
--- a/libxfs/xfs_format.h
+++ b/libxfs/xfs_format.h
@@ -97,7 +97,7 @@
 	uint32_t	sb_blocksize;	/* logical block size, bytes */
 	xfs_rfsblock_t	sb_dblocks;	/* number of data blocks */
 	xfs_rfsblock_t	sb_rblocks;	/* number of realtime blocks */
-	xfs_rtblock_t	sb_rextents;	/* number of realtime extents */
+	xfs_rtbxlen_t	sb_rextents;	/* number of realtime extents */
 	uuid_t		sb_uuid;	/* user-visible file system unique id */
 	xfs_fsblock_t	sb_logstart;	/* starting block of log if internal */
 	xfs_ino_t	sb_rootino;	/* root inode number */
diff --git a/libxfs/xfs_rtbitmap.h b/libxfs/xfs_rtbitmap.h
index e2ea6d3..b0a81fb 100644
--- a/libxfs/xfs_rtbitmap.h
+++ b/libxfs/xfs_rtbitmap.h
@@ -13,7 +13,7 @@
  */
 struct xfs_rtalloc_rec {
 	xfs_rtblock_t		ar_startext;
-	xfs_rtblock_t		ar_extcount;
+	xfs_rtbxlen_t		ar_extcount;
 };
 
 typedef int (*xfs_rtalloc_query_range_fn)(
diff --git a/libxfs/xfs_types.h b/libxfs/xfs_types.h
index 0856997..a2fb880 100644
--- a/libxfs/xfs_types.h
+++ b/libxfs/xfs_types.h
@@ -32,6 +32,7 @@
 typedef uint64_t	xfs_rtblock_t;	/* extent (block) in realtime area */
 typedef uint64_t	xfs_fileoff_t;	/* block number in a file */
 typedef uint64_t	xfs_filblks_t;	/* number of blocks in a file */
+typedef uint64_t	xfs_rtbxlen_t;	/* rtbitmap extent length in rtextents */
 
 typedef int64_t		xfs_srtblock_t;	/* signed version of xfs_rtblock_t */