diff --git a/drivers/net/ethernet/netronome/nfp/flower/cmsg.c b/drivers/net/ethernet/netronome/nfp/flower/cmsg.c
index 56b22ea32474..cf9e1118ee8f 100644
--- a/drivers/net/ethernet/netronome/nfp/flower/cmsg.c
+++ b/drivers/net/ethernet/netronome/nfp/flower/cmsg.c
@@ -45,11 +45,9 @@ nfp_flower_cmsg_mac_repr_start(struct nfp_app *app, unsigned int num_ports)
 {
 	struct nfp_flower_cmsg_mac_repr *msg;
 	struct sk_buff *skb;
-	unsigned int size;
 
-	size = sizeof(*msg) + num_ports * sizeof(msg->ports[0]);
-	skb = nfp_flower_cmsg_alloc(app, size, NFP_FLOWER_CMSG_TYPE_MAC_REPR,
-				    GFP_KERNEL);
+	skb = nfp_flower_cmsg_alloc(app, struct_size(msg, ports, num_ports),
+				    NFP_FLOWER_CMSG_TYPE_MAC_REPR, GFP_KERNEL);
 	if (!skb)
 		return NULL;