diff --git a/include/net/dsa.h b/include/net/dsa.h
index 9e55938853571..929bcaec4d41a 100644
--- a/include/net/dsa.h
+++ b/include/net/dsa.h
@@ -159,6 +159,9 @@ struct dsa_switch_tree {
 	 */
 	struct net_device **lags;
 	unsigned int lags_len;
+
+	/* Track the largest switch index within a tree */
+	unsigned int last_switch;
 };
 
 #define dsa_lags_foreach_id(_id, _dst)				\
diff --git a/net/dsa/dsa2.c b/net/dsa/dsa2.c
index 185629f27f803..de5e93ba2a9d6 100644
--- a/net/dsa/dsa2.c
+++ b/net/dsa/dsa2.c
@@ -1265,6 +1265,9 @@ static int dsa_switch_parse_member_of(struct dsa_switch *ds,
 		return -EEXIST;
 	}
 
+	if (ds->dst->last_switch < ds->index)
+		ds->dst->last_switch = ds->index;
+
 	return 0;
 }