diff --git a/include/haproxy/quic_cc-t.h b/include/haproxy/quic_cc-t.h
index e67817239..39699e450 100644
--- a/include/haproxy/quic_cc-t.h
+++ b/include/haproxy/quic_cc-t.h
@@ -96,8 +96,8 @@ struct quic_cc_path {
 	/* Packet loss detection information. */
 	struct quic_loss loss;
 
-	/* MTU. */
-	size_t mtu;
+	/* MTU. Must be constant for GSO support. */
+	const size_t mtu;
 	/* Congestion window. */
 	uint64_t cwnd;
 	/* The current maximum congestion window value reached. */
diff --git a/include/haproxy/quic_cc.h b/include/haproxy/quic_cc.h
index 721feca78..269a93101 100644
--- a/include/haproxy/quic_cc.h
+++ b/include/haproxy/quic_cc.h
@@ -84,7 +84,7 @@ static inline void quic_cc_path_init(struct quic_cc_path *path, int ipv4, unsign
 
 	max_dgram_sz = ipv4 ? QUIC_INITIAL_IPV4_MTU : QUIC_INITIAL_IPV6_MTU;
 	quic_loss_init(&path->loss);
-	path->mtu = max_dgram_sz;
+	*(size_t *)&path->mtu = max_dgram_sz;
 	path->cwnd = QUIC_MIN(10 * max_dgram_sz, QUIC_MAX(max_dgram_sz << 1, 14720U));
 	path->mcwnd = path->cwnd;
 	path->max_cwnd = max_cwnd;