diff --git a/net/rxrpc/input.c b/net/rxrpc/input.c
index af8ce64f4162..04213a65c1ac 100644
--- a/net/rxrpc/input.c
+++ b/net/rxrpc/input.c
@@ -868,6 +868,16 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb,
 				  rxrpc_propose_ack_respond_to_ack);
 	}
 
+	/* Discard any out-of-order or duplicate ACKs. */
+	if (before_eq(sp->hdr.serial, call->acks_latest)) {
+		_debug("discard ACK %d <= %d",
+		       sp->hdr.serial, call->acks_latest);
+		return;
+	}
+	call->acks_latest_ts = skb->tstamp;
+	call->acks_latest = sp->hdr.serial;
+
+	/* Parse rwind and mtu sizes if provided. */
 	ioffset = offset + nr_acks + 3;
 	if (skb->len >= ioffset + sizeof(buf.info)) {
 		if (skb_copy_bits(skb, ioffset, &buf.info, sizeof(buf.info)) < 0)
@@ -889,15 +899,6 @@ static void rxrpc_input_ack(struct rxrpc_call *call, struct sk_buff *skb,
 		return;
 	}
 
-	/* Discard any out-of-order or duplicate ACKs. */
-	if (before_eq(sp->hdr.serial, call->acks_latest)) {
-		_debug("discard ACK %d <= %d",
-		       sp->hdr.serial, call->acks_latest);
-		return;
-	}
-	call->acks_latest_ts = skb->tstamp;
-	call->acks_latest = sp->hdr.serial;
-
 	if (before(hard_ack, call->tx_hard_ack) ||
 	    after(hard_ack, call->tx_top))
 		return rxrpc_proto_abort("AKW", call, 0);