diff --git a/sys/kern/vfs_mount.c.zfssnap b/sys/kern/vfs_mount.c
--- a/sys/kern/vfs_mount.c.zfssnap
+++ b/sys/kern/vfs_mount.c
@@ -3141,3 +3141,29 @@
 	}
 	mtx_unlock(&mountlist_mtx);
 }
+
+/*
+ * Clone the mnt_exjail field to a new mount point.
+ */
+void
+vfs_exjail_clone(struct mount *inmp, struct mount *outmp)
+{
+	struct ucred *cr;
+
+	MNT_ILOCK(inmp);
+	cr = inmp->mnt_exjail;
+	if (cr != NULL) {
+		crhold(cr);
+		MNT_IUNLOCK(inmp);
+		MNT_ILOCK(outmp);
+		if (outmp->mnt_exjail == NULL) {
+			outmp->mnt_exjail = cr;
+			atomic_add_int(&cr->cr_prison->pr_exportcnt, 1);
+			cr = NULL;
+		}
+		MNT_IUNLOCK(outmp);
+		if (cr != NULL)
+			crfree(cr);
+	} else
+		MNT_IUNLOCK(inmp);
+}
diff --git a/sys/sys/mount.h.zfssnap b/sys/sys/mount.h
--- a/sys/sys/mount.h.zfssnap
+++ b/sys/sys/mount.h
@@ -1017,6 +1017,7 @@
 	    (struct mount *, struct netexport *, struct export_args *);
 void	vfs_periodic(struct mount *, int);
 int	vfs_busy(struct mount *, int);
+void	vfs_exjail_clone(struct mount *, struct mount *);
 void	vfs_exjail_delete(struct prison *);
 int	vfs_export			 /* process mount export info */
 	    (struct mount *, struct export_args *, bool);