Index: uspace/srv/fs/mfs/mfs_ops.c
===================================================================
--- uspace/srv/fs/mfs/mfs_ops.c	(revision f456ab20f3246734ac48ab3829ac2f21b712909c)
+++ uspace/srv/fs/mfs/mfs_ops.c	(revision 85ff862c8e671c25e6519e7b413df4741a121b5a)
@@ -249,4 +249,17 @@
 				    MFS_MAX_NAME_LEN;
 	}
+
+	if (sbi->log2_zone_size != 0) {
+		/* In MFS, file space is allocated per zones.
+		 * Zones are a collection of consecutive blocks on disk.
+		 *
+		 * The current MFS implementation supports only filesystems
+		 * where the size of a zone is equal to the
+		 * size of a block.
+		 */
+		rc = ENOTSUP;
+		goto out_error;
+	}
+
 	sbi->itable_off = 2 + sbi->ibmap_blocks + sbi->zbmap_blocks;