diff --git a/slirp/bootp.c b/slirp/bootp.c
index 261762a..3e4e881 100644
--- a/slirp/bootp.c
+++ b/slirp/bootp.c
@@ -293,7 +293,7 @@
         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;