diff --git a/include/fsgeom.h b/include/fsgeom.h
index 7837c700..771732f2 100644
--- a/include/fsgeom.h
+++ b/include/fsgeom.h
@@ -32,6 +32,9 @@ struct xfs_fd {
 
 	/* log2 of sb_inopblock */
 	unsigned int		inopblog;
+
+	/* bits for agino in inum */
+	unsigned int		aginolog;
 };
 
 /* Static initializers */
@@ -41,4 +44,58 @@ struct xfs_fd {
 int xfd_prepare_geometry(struct xfs_fd *xfd);
 int xfd_close(struct xfs_fd *xfd);
 
+/* Convert AG number and AG inode number into fs inode number. */
+static inline uint64_t
+cvt_agino_to_ino(
+	const struct xfs_fd	*xfd,
+	uint32_t		agno,
+	uint32_t		agino)
+{
+	return ((uint64_t)agno << xfd->aginolog) + agino;
+}
+
+/* Convert fs inode number into AG number. */
+static inline uint32_t
+cvt_ino_to_agno(
+	const struct xfs_fd	*xfd,
+	uint64_t		ino)
+{
+	return ino >> xfd->aginolog;
+}
+
+/* Convert fs inode number into AG inode number. */
+static inline uint32_t
+cvt_ino_to_agino(
+	const struct xfs_fd	*xfd,
+	uint64_t		ino)
+{
+	return ino & ((1ULL << xfd->aginolog) - 1);
+}
+
+/*
+ * Convert a linear fs block offset number into bytes.  This is the runtime
+ * equivalent of XFS_FSB_TO_B, which means that it is /not/ for segmented fsbno
+ * format (= agno | agbno) that we use internally for the data device.
+ */
+static inline uint64_t
+cvt_off_fsb_to_b(
+	const struct xfs_fd	*xfd,
+	uint64_t		fsb)
+{
+	return fsb << xfd->blocklog;
+}
+
+/*
+ * Convert bytes into a (rounded down) linear fs block offset number.  This is
+ * the runtime equivalent of XFS_B_TO_FSBT.  It does not produce segmented
+ * fsbno numbers (= agno | agbno).
+ */
+static inline uint64_t
+cvt_b_to_off_fsbt(
+	const struct xfs_fd	*xfd,
+	uint64_t		bytes)
+{
+	return bytes >> xfd->blocklog;
+}
+
 #endif /* _LIBFROG_FSGEOM_H_ */
diff --git a/libfrog/fsgeom.c b/libfrog/fsgeom.c
index b7e2b2f8..39604556 100644
--- a/libfrog/fsgeom.c
+++ b/libfrog/fsgeom.c
@@ -112,6 +112,7 @@ xfd_prepare_geometry(
 	xfd->blocklog = highbit32(xfd->fsgeom.blocksize);
 	xfd->inodelog = highbit32(xfd->fsgeom.inodesize);
 	xfd->inopblog = xfd->blocklog - xfd->inodelog;
+	xfd->aginolog = xfd->agblklog + xfd->inopblog;
 	return 0;
 }
 
diff --git a/scrub/fscounters.c b/scrub/fscounters.c
index ac898764..ea6af156 100644
--- a/scrub/fscounters.c
+++ b/scrub/fscounters.c
@@ -91,8 +91,8 @@ xfs_count_ag_inodes(
 				minor(ctx->fsinfo.fs_datadev),
 				agno);
 
-	ag_ino = (__u64)agno << (ctx->mnt.inopblog + ctx->mnt.agblklog);
-	next_ag_ino = (__u64)(agno + 1) << (ctx->mnt.inopblog + ctx->mnt.agblklog);
+	ag_ino = cvt_agino_to_ino(&ctx->mnt, agno, 0);
+	next_ag_ino = cvt_agino_to_ino(&ctx->mnt, agno + 1, 0);
 
 	moveon = xfs_count_inodes_range(ctx, descr, ag_ino, next_ag_ino - 1,
 			&ci->counters[agno]);
diff --git a/scrub/inodes.c b/scrub/inodes.c
index 873ad425..700e5200 100644
--- a/scrub/inodes.c
+++ b/scrub/inodes.c
@@ -228,8 +228,8 @@ xfs_scan_ag_inodes(
 				minor(ctx->fsinfo.fs_datadev),
 				agno);
 
-	ag_ino = (__u64)agno << (ctx->mnt.inopblog + ctx->mnt.agblklog);
-	next_ag_ino = (__u64)(agno + 1) << (ctx->mnt.inopblog + ctx->mnt.agblklog);
+	ag_ino = cvt_agino_to_ino(&ctx->mnt, agno, 0);
+	next_ag_ino = cvt_agino_to_ino(&ctx->mnt, agno + 1, 0);
 
 	moveon = xfs_iterate_inodes_range(ctx, descr, ctx->fshandle, ag_ino,
 			next_ag_ino - 1, si->fn, si->arg);
diff --git a/scrub/phase3.c b/scrub/phase3.c
index 579e08c3..8c02f1cb 100644
--- a/scrub/phase3.c
+++ b/scrub/phase3.c
@@ -52,8 +52,8 @@ xfs_scrub_inode_vfs_error(
 	xfs_agino_t		agino;
 	int			old_errno = errno;
 
-	agno = bstat->bs_ino / (1ULL << (ctx->mnt.inopblog + ctx->mnt.agblklog));
-	agino = bstat->bs_ino % (1ULL << (ctx->mnt.inopblog + ctx->mnt.agblklog));
+	agno = cvt_ino_to_agno(&ctx->mnt, bstat->bs_ino);
+	agino = cvt_ino_to_agino(&ctx->mnt, bstat->bs_ino);
 	snprintf(descr, DESCR_BUFSZ, _("inode %"PRIu64" (%u/%u)"),
 			(uint64_t)bstat->bs_ino, agno, agino);
 	errno = old_errno;
@@ -77,7 +77,7 @@ xfs_scrub_inode(
 	int			error;
 
 	xfs_action_list_init(&alist);
-	agno = bstat->bs_ino / (1ULL << (ctx->mnt.inopblog + ctx->mnt.agblklog));
+	agno = cvt_ino_to_agno(&ctx->mnt, bstat->bs_ino);
 	background_sleep();
 
 	/* Try to open the inode to pin it. */
diff --git a/scrub/phase5.c b/scrub/phase5.c
index 36ec27b3..f3ee22e6 100644
--- a/scrub/phase5.c
+++ b/scrub/phase5.c
@@ -239,8 +239,8 @@ xfs_scrub_connections(
 	int			fd = -1;
 	int			error;
 
-	agno = bstat->bs_ino / (1ULL << (ctx->mnt.inopblog + ctx->mnt.agblklog));
-	agino = bstat->bs_ino % (1ULL << (ctx->mnt.inopblog + ctx->mnt.agblklog));
+	agno = cvt_ino_to_agno(&ctx->mnt, bstat->bs_ino);
+	agino = cvt_ino_to_agino(&ctx->mnt, bstat->bs_ino);
 	snprintf(descr, DESCR_BUFSZ, _("inode %"PRIu64" (%u/%u)"),
 			(uint64_t)bstat->bs_ino, agno, agino);
 	background_sleep();
diff --git a/scrub/phase6.c b/scrub/phase6.c
index 48971270..5628b926 100644
--- a/scrub/phase6.c
+++ b/scrub/phase6.c
@@ -547,7 +547,8 @@ xfs_estimate_verify_work(
 	if (!moveon)
 		return moveon;
 
-	*items = ((d_blocks - d_bfree) + (r_blocks - r_bfree)) << ctx->mnt.blocklog;
+	*items = cvt_off_fsb_to_b(&ctx->mnt,
+			(d_blocks - d_bfree) + (r_blocks - r_bfree));
 	*nr_threads = disk_heads(ctx->datadev);
 	*rshift = 20;
 	return moveon;
diff --git a/scrub/phase7.c b/scrub/phase7.c
index 41a77356..8a028e19 100644
--- a/scrub/phase7.c
+++ b/scrub/phase7.c
@@ -148,11 +148,11 @@ xfs_scan_summary(
 	 * filesystem treats them as "free", but since we scanned
 	 * them, we'll consider them used.
 	 */
-	d_bfree -= totalcount.agbytes >> ctx->mnt.blocklog;
+	d_bfree -= cvt_b_to_off_fsbt(&ctx->mnt, totalcount.agbytes);
 
 	/* Report on what we found. */
-	used_data = (d_blocks - d_bfree) << ctx->mnt.blocklog;
-	used_rt = (r_blocks - r_bfree) << ctx->mnt.blocklog;
+	used_data = cvt_off_fsb_to_b(&ctx->mnt, d_blocks - d_bfree);
+	used_rt = cvt_off_fsb_to_b(&ctx->mnt, r_blocks - r_bfree);
 	used_files = f_files - f_free;
 	stat_data = totalcount.dbytes;
 	stat_rt = totalcount.rbytes;
