diff --git a/slirp/cksum.c b/slirp/cksum.c
index a044ec17cc..c3b45f7b3d 100644
--- a/slirp/cksum.c
+++ b/slirp/cksum.c
@@ -42,7 +42,8 @@
  */
 
 #define ADDCARRY(x)  (x > 65535 ? x -= 65535 : x)
-#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1]; ADDCARRY(sum);}
+#define REDUCE {l_util.l = sum; sum = l_util.s[0] + l_util.s[1];        \
+        (void)ADDCARRY(sum);}
 
 int cksum(struct mbuf *m, int len)
 {