diff --git a/net/sched/cls_flow.c b/net/sched/cls_flow.c
index 339c664beff6..ab364e4e4686 100644
--- a/net/sched/cls_flow.c
+++ b/net/sched/cls_flow.c
@@ -503,8 +503,16 @@ static int flow_change(struct net *net, struct sk_buff *in_skb,
 		}
 
 		if (TC_H_MAJ(baseclass) == 0) {
-			struct Qdisc *q = tcf_block_q(tp->chain->block);
+			struct tcf_block *block = tp->chain->block;
+			struct Qdisc *q;
 
+			if (tcf_block_shared(block)) {
+				NL_SET_ERR_MSG(extack,
+					       "Must specify baseclass when attaching flow filter to block");
+				goto err2;
+			}
+
+			q = tcf_block_q(block);
 			baseclass = TC_H_MAKE(q->handle, baseclass);
 		}
 		if (TC_H_MIN(baseclass) == 0)