diff --git a/pkg/operator/ceph/object/bucket/provisioner.go b/pkg/operator/ceph/object/bucket/provisioner.go
index 6e87c27b0..2ea1b5db3 100644
--- a/pkg/operator/ceph/object/bucket/provisioner.go
+++ b/pkg/operator/ceph/object/bucket/provisioner.go
@@ -68,7 +68,10 @@ func (p Provisioner) GenerateUserID(obc *v1alpha1.ObjectBucketClaim, ob *v1alpha
 		return getCephUser(ob), nil
 	}
 
-	username := p.genUserName(obc.Name, obc.Namespace)
+	username, err := p.genUserName(obc.Name, obc.Namespace)
+	if err != nil {
+		return "", errors.Wrap(err, "failed to generate user id for OBC")
+	}
 
 	return username, nil
 }
diff --git a/pkg/operator/ceph/object/bucket/rgw-handlers.go b/pkg/operator/ceph/object/bucket/rgw-handlers.go
index fe1c4ea74..c1f72bcc5 100644
--- a/pkg/operator/ceph/object/bucket/rgw-handlers.go
+++ b/pkg/operator/ceph/object/bucket/rgw-handlers.go
@@ -47,10 +47,15 @@ func (p *Provisioner) createCephUser(username string) (accKey string, secKey str
 	return u.Keys[0].AccessKey, u.Keys[0].SecretKey, nil
 }
 
-func (p *Provisioner) genUserName(obcName, obcNamespace string) string {
-	// user name can be deterministically generated by obc name and namespace
-	// since there can't be 2 obcs in the same namespace with the same name, this will not collide
-	return "obc-" + obcNamespace + "-" + obcName
+func (p *Provisioner) genUserName(obcName, obcNamespace string) (string, error) {
+	// user name can be deterministically generated by obc name and namespace. since there can't be
+	// 2 obcs in the same namespace w/ the same name, this won't collide w/in the same k8s cluster.
+	// However, it can collide in multisite setups, so use the Ceph cluster FSID
+	fsid := p.clusterInfo.FSID
+	if p.clusterInfo.FSID == "" {
+		return "", errors.Errorf("failed to find ceph cluster FSID")
+	}
+	return "obc-" + obcNamespace + "-" + obcName + "-" + fsid, nil
 }
 
 // Delete the user and bucket created by OBC with help of radosgw-admin commands