diff --git a/slirp/bootp.c b/slirp/bootp.c
index 755072d..30cb05e 100644
--- a/slirp/bootp.c
+++ b/slirp/bootp.c
@@ -225,7 +225,8 @@
     }
     *q++ = RFC1533_END;
     
-    m->m_len = sizeof(struct bootp_t);
+    m->m_len = sizeof(struct bootp_t) - 
+        sizeof(struct ip) - sizeof(struct udphdr);
     udp_output2(NULL, m, &saddr, &daddr, IPTOS_LOWDELAY);
 }