diff --git a/slirp/bootp.c b/slirp/bootp.c
index 261762a260..3e4e8810be 100644
--- a/slirp/bootp.c
+++ b/slirp/bootp.c
@@ -293,7 +293,7 @@ static void bootp_reply(Slirp *slirp, const struct bootp_t *bp)
         memcpy(q, nak_msg, sizeof(nak_msg) - 1);
         q += sizeof(nak_msg) - 1;
     }
-    *q++ = RFC1533_END;
+    *q = RFC1533_END;
 
     daddr.sin_addr.s_addr = 0xffffffffu;
 
diff --git a/slirp/cksum.c b/slirp/cksum.c
index 34977ffc03..a044ec17cc 100644
--- a/slirp/cksum.c
+++ b/slirp/cksum.c
@@ -68,7 +68,9 @@ int cksum(struct mbuf *m, int len)
 
 	if (len < mlen)
 	   mlen = len;
+#ifdef DEBUG
 	len -= mlen;
+#endif
 	/*
 	 * Force to even boundary.
 	 */
diff --git a/slirp/tcp_subr.c b/slirp/tcp_subr.c
index 7851307fa0..0a370f101e 100644
--- a/slirp/tcp_subr.c
+++ b/slirp/tcp_subr.c
@@ -857,7 +857,7 @@ tcp_emu(struct socket *so, struct mbuf *m)
 				if (p == 7071)
 				   p = 0;
 				*(u_char *)bptr++ = (p >> 8) & 0xff;
-				*(u_char *)bptr++ = p & 0xff;
+                                *(u_char *)bptr = p & 0xff;
 				ra = 0;
 				return 1;   /* port redirected, we're done */
 				break;