diff --git a/net/iucv/af_iucv.c b/net/iucv/af_iucv.c
index 4e5cc9da6e06..db261ecd19af 100644
--- a/net/iucv/af_iucv.c
+++ b/net/iucv/af_iucv.c
@@ -210,12 +210,6 @@ static int afiucv_hs_send(struct iucv_message *imsg, struct sock *sock,
 	phs_hdr->flags = flags;
 	if (flags == AF_IUCV_FLAG_SYN)
 		phs_hdr->window = iucv->msglimit;
-	else if ((flags == AF_IUCV_FLAG_WIN) || !flags) {
-		confirm_recv = atomic_read(&iucv->msg_recv);
-		phs_hdr->window = confirm_recv;
-		if (confirm_recv)
-			phs_hdr->flags = phs_hdr->flags | AF_IUCV_FLAG_WIN;
-	}
 	memcpy(phs_hdr->destUserID, iucv->dst_user_id, 8);
 	memcpy(phs_hdr->destAppName, iucv->dst_name, 8);
 	memcpy(phs_hdr->srcUserID, iucv->src_user_id, 8);
@@ -250,13 +244,22 @@ static int afiucv_hs_send(struct iucv_message *imsg, struct sock *sock,
 	}
 	skb->protocol = cpu_to_be16(ETH_P_AF_IUCV);
 
+	/* Claim the receive credit here, not while building the header: every
+	 * way this frame can be dropped has now been ruled out, so the window
+	 * is zeroed only for as long as the transmit itself takes.
+	 */
+	if (flags == AF_IUCV_FLAG_WIN || !flags) {
+		confirm_recv = atomic_xchg(&iucv->msg_recv, 0);
+		phs_hdr->window = confirm_recv;
+		if (confirm_recv)
+			phs_hdr->flags = phs_hdr->flags | AF_IUCV_FLAG_WIN;
+	}
+
 	atomic_inc(&iucv->skbs_in_xmit);
 	err = dev_queue_xmit(skb);
 	if (net_xmit_eval(err)) {
 		atomic_dec(&iucv->skbs_in_xmit);
-	} else {
-		atomic_sub(confirm_recv, &iucv->msg_recv);
-		WARN_ON(atomic_read(&iucv->msg_recv) < 0);
+		atomic_add(confirm_recv, &iucv->msg_recv);
 	}
 	return net_xmit_eval(err);
 
@@ -1241,6 +1244,7 @@ static int iucv_sock_recvmsg(struct socket *sock, struct msghdr *msg,
 	struct iucv_sock *iucv = iucv_sk(sk);
 	unsigned int copied, rlen;
 	struct sk_buff *skb, *rskb, *cskb;
+	bool send_win = false;
 	int err = 0;
 	u32 offset;
 
@@ -1331,16 +1335,20 @@ static int iucv_sock_recvmsg(struct socket *sock, struct msghdr *msg,
 		if (skb_queue_empty(&iucv->backlog_skb_q)) {
 			if (!list_empty(&iucv->message_q.list))
 				iucv_process_message_q(sk);
-			if (atomic_read(&iucv->msg_recv) >=
-							iucv->msglimit / 2) {
-				err = iucv_send_ctrl(sk, AF_IUCV_FLAG_WIN);
-				if (err) {
-					sk->sk_state = IUCV_DISCONN;
-					sk->sk_state_change(sk);
-				}
-			}
+			if (iucv->transport == AF_IUCV_TRANS_HIPER &&
+			    atomic_read(&iucv->msg_recv) >=
+							iucv->msglimit / 2)
+				send_win = true;
 		}
 		spin_unlock_bh(&iucv->message_q.lock);
+
+		if (send_win) {
+			err = iucv_send_ctrl(sk, AF_IUCV_FLAG_WIN);
+			if (err) {
+				sk->sk_state = IUCV_DISCONN;
+				sk->sk_state_change(sk);
+			}
+		}
 	}
 
 done: