diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index ca8d3c87..c82aed9f 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -970,7 +970,7 @@ tcp_receive(struct tcp_pcb *pcb)
     /* Update window. */
     if (TCP_SEQ_LT(pcb->snd_wl1, seqno) ||
        (pcb->snd_wl1 == seqno && TCP_SEQ_LT(pcb->snd_wl2, ackno)) ||
-       (pcb->snd_wl2 == ackno && SND_WND_SCALE(pcb, tcphdr->wnd) > pcb->snd_wnd)) {
+       (pcb->snd_wl2 == ackno && (u32_t)SND_WND_SCALE(pcb, tcphdr->wnd) > pcb->snd_wnd)) {
       pcb->snd_wnd = SND_WND_SCALE(pcb, tcphdr->wnd); 
       /* keep track of the biggest window announced by the remote host to calculate
          the maximum segment size */