diff --git a/src/include/lwip/api.h b/src/include/lwip/api.h
index f8426a7d..c2afaf26 100644
--- a/src/include/lwip/api.h
+++ b/src/include/lwip/api.h
@@ -370,7 +370,7 @@ err_t   netconn_err(struct netconn *conn);
 #define netconn_recv_bufsize(conn)      ((conn)->recv_bufsize)
 
 #define netconn_set_flags(conn, set_flags)     do { (conn)->flags = (u8_t)((conn)->flags |  (set_flags)); } while(0)
-#define netconn_clear_flags(conn, clr_flags)   do { (conn)->flags = (u8_t)((conn)->flags & ~(clr_flags)); } while(0)
+#define netconn_clear_flags(conn, clr_flags)   do { (conn)->flags = (u8_t)((conn)->flags & (u8_t)(~(clr_flags) & 0xff)); } while(0)
 #define netconn_is_flag_set(conn, flag)        (((conn)->flags & (flag)) != 0)
 
 /** Set the blocking status of netconn calls (@todo: write/send is missing) */
diff --git a/src/include/lwip/netif.h b/src/include/lwip/netif.h
index 86d1485a..911196ab 100644
--- a/src/include/lwip/netif.h
+++ b/src/include/lwip/netif.h
@@ -450,7 +450,7 @@ void netif_set_gw(struct netif *netif, const ip4_addr_t *gw);
 #endif /* LWIP_IPV4 */
 
 #define netif_set_flags(netif, set_flags)     do { (netif)->flags = (u8_t)((netif)->flags |  (set_flags)); } while(0)
-#define netif_clear_flags(netif, clr_flags)   do { (netif)->flags = (u8_t)((netif)->flags & ~(clr_flags)); } while(0)
+#define netif_clear_flags(netif, clr_flags)   do { (netif)->flags = (u8_t)((netif)->flags & (u8_t)(~(clr_flags) & 0xff)); } while(0)
 #define netif_is_flag_set(nefif, flag)        (((netif)->flags & (flag)) != 0)
 
 void netif_set_up(struct netif *netif);
diff --git a/src/include/lwip/raw.h b/src/include/lwip/raw.h
index c94f3bf4..b129bd3b 100644
--- a/src/include/lwip/raw.h
+++ b/src/include/lwip/raw.h
@@ -119,7 +119,7 @@ void             raw_recv       (struct raw_pcb *pcb, raw_recv_fn recv, void *re
 #define          raw_setflags(pcb,f)  ((pcb)->flags = (f))
 
 #define          raw_set_flags(pcb, set_flags)     do { (pcb)->flags = (u8_t)((pcb)->flags |  (set_flags)); } while(0)
-#define          raw_clear_flags(pcb, clr_flags)   do { (pcb)->flags = (u8_t)((pcb)->flags & ~(clr_flags)); } while(0)
+#define          raw_clear_flags(pcb, clr_flags)   do { (pcb)->flags = (u8_t)((pcb)->flags & (u8_t)(~(clr_flags) & 0xff)); } while(0)
 #define          raw_is_flag_set(pcb, flag)        (((pcb)->flags & (flag)) != 0)
 
 #define raw_init() /* Compatibility define, no init needed. */
diff --git a/src/include/lwip/tcp.h b/src/include/lwip/tcp.h
index b145781f..daf75994 100644
--- a/src/include/lwip/tcp.h
+++ b/src/include/lwip/tcp.h
@@ -204,6 +204,7 @@ struct tcp_pcb_ext_args {
 #endif
 
 typedef u16_t tcpflags_t;
+#define TCP_ALLFLAGS 0xffffU
 
 /**
  * members common to struct tcp_pcb and struct tcp_listen_pcb
@@ -420,7 +421,7 @@ void             tcp_accept  (struct tcp_pcb *pcb, tcp_accept_fn accept);
 void             tcp_poll    (struct tcp_pcb *pcb, tcp_poll_fn poll, u8_t interval);
 
 #define          tcp_set_flags(pcb, set_flags)     do { (pcb)->flags = (tcpflags_t)((pcb)->flags |  (set_flags)); } while(0)
-#define          tcp_clear_flags(pcb, clr_flags)   do { (pcb)->flags = (tcpflags_t)((pcb)->flags & ~(clr_flags)); } while(0)
+#define          tcp_clear_flags(pcb, clr_flags)   do { (pcb)->flags = (tcpflags_t)((pcb)->flags & (tcpflags_t)(~(clr_flags) & TCP_ALLFLAGS)); } while(0)
 #define          tcp_is_flag_set(pcb, flag)        (((pcb)->flags & (flag)) != 0)
 
 #if LWIP_TCP_TIMESTAMPS
diff --git a/src/include/lwip/udp.h b/src/include/lwip/udp.h
index 4f4a36d3..b1c78e58 100644
--- a/src/include/lwip/udp.h
+++ b/src/include/lwip/udp.h
@@ -156,7 +156,7 @@ err_t            udp_sendto_if_src_chksum(struct udp_pcb *pcb, struct pbuf *p,
 #define          udp_setflags(pcb, f)  ((pcb)->flags = (f))
 
 #define          udp_set_flags(pcb, set_flags)     do { (pcb)->flags = (u8_t)((pcb)->flags |  (set_flags)); } while(0)
-#define          udp_clear_flags(pcb, clr_flags)   do { (pcb)->flags = (u8_t)((pcb)->flags & ~(clr_flags)); } while(0)
+#define          udp_clear_flags(pcb, clr_flags)   do { (pcb)->flags = (u8_t)((pcb)->flags & (u8_t)(~(clr_flags) & 0xff)); } while(0)
 #define          udp_is_flag_set(pcb, flag)        (((pcb)->flags & (flag)) != 0)
 
 /* The following functions are the lower layer interface to UDP. */