diff --git a/Create.c b/Create.c
index 2c0b17e..0ff1922 100644
--- a/Create.c
+++ b/Create.c
@@ -899,8 +899,13 @@ int Create(struct supertype *st, char *mddev,
 				else
 					inf->disk.state = 0;
 
-				if (dv->writemostly == FlagSet)
-					inf->disk.state |= (1<<MD_DISK_WRITEMOSTLY);
+				if (dv->writemostly == FlagSet) {
+					if (major_num == BITMAP_MAJOR_CLUSTERED) {
+						pr_err("Can not set %s --write-mostly with a clustered bitmap\n",dv->devname);
+						goto abort_locked;
+					} else
+						inf->disk.state |= (1<<MD_DISK_WRITEMOSTLY);
+				}
 				if (dv->failfast == FlagSet)
 					inf->disk.state |= (1<<MD_DISK_FAILFAST);
 
diff --git a/Grow.c b/Grow.c
index 7506ab4..70f26c7 100644
--- a/Grow.c
+++ b/Grow.c
@@ -430,6 +430,11 @@ int Grow_addbitmap(char *devname, int fd, struct context *c, struct shape *s)
 			dv = map_dev(disk.major, disk.minor, 1);
 			if (!dv)
 				continue;
+			if (((disk.state & (1 << MD_DISK_WRITEMOSTLY)) == 0) &&
+			   (strcmp(s->bitmap_file, "clustered") == 0)) {
+				pr_err("%s disks marked write-mostly are not supported with clustered bitmap\n",devname);
+				return 1;
+			}
 			fd2 = dev_open(dv, O_RDWR);
 			if (fd2 < 0)
 				continue;