diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index 3c94763a..2305a3cb 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -1200,22 +1200,14 @@ tcp_receive(struct tcp_pcb *pcb)
           u8_t num_seg = (pcb->flags & TF_RTO) ? 1 : 2;
           /* RFC 3465, section 2.2 Slow Start */
           increase = LWIP_MIN(acked, (tcpwnd_size_t)(num_seg * pcb->mss));
-          if (pcb->cwnd + increase > pcb->cwnd) {
-            pcb->cwnd += increase;
-          }
+          TCP_WND_INC(pcb->cwnd, increase);
           LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_receive: slow start cwnd %"TCPWNDSIZE_F"\n", pcb->cwnd));
         } else {
-          tcpwnd_size_t new_cwnd = pcb->cwnd;
           /* RFC 3465, section 2.1 Congestion Avoidance */
-          if (pcb->bytes_acked + acked > pcb->bytes_acked) {
-            pcb->bytes_acked += acked;
-            if (pcb->bytes_acked >= pcb->cwnd) {
-              pcb->bytes_acked -= pcb->cwnd;
-              new_cwnd = pcb->cwnd + pcb->mss;
-            }
-          }
-          if (new_cwnd > pcb->cwnd) {
-            pcb->cwnd = new_cwnd;
+          TCP_WND_INC(pcb->bytes_acked, acked);
+          if (pcb->bytes_acked >= pcb->cwnd) {
+            pcb->bytes_acked -= pcb->cwnd;
+            TCP_WND_INC(pcb->cwnd, pcb->mss);
           }
           LWIP_DEBUGF(TCP_CWND_DEBUG, ("tcp_receive: congestion avoidance cwnd %"TCPWNDSIZE_F"\n", pcb->cwnd));
         }
diff --git a/src/include/lwip/tcp.h b/src/include/lwip/tcp.h
index ad192390..e5e05693 100644
--- a/src/include/lwip/tcp.h
+++ b/src/include/lwip/tcp.h
@@ -143,6 +143,14 @@ typedef err_t (*tcp_connected_fn)(void *arg, struct tcp_pcb *tpcb, err_t err);
 #define TCPWND16(x)             (x)
 #define TCP_WND_MAX(pcb)        TCP_WND
 #endif
+/* Increments a tcpwnd_size_t and holds at max value rather than rollover */
+#define TCP_WND_INC(wnd, inc)   do { \
+                                  if ((tcpwnd_size_t)(wnd + inc) >= wnd) { \
+                                    wnd += inc; \
+                                  } else { \
+                                    wnd = (tcpwnd_size_t)-1; \
+                                  } \
+                                } while(0)
 
 #if LWIP_WND_SCALE || TCP_LISTEN_BACKLOG || LWIP_TCP_TIMESTAMPS
 typedef u16_t tcpflags_t;