diff --git a/src/ip_input.c b/src/ip_input.c
index 50c7657d55e05762f2559853afa186e788573da8..8c75d91495dfdb32f00aea66acd3b5a5936df858 100644
--- a/src/ip_input.c
+++ b/src/ip_input.c
@@ -326,6 +326,8 @@ insert:
     q = fp->frag_link.next;
     m = dtom(slirp, q);
 
+    int was_ext = m->m_flags & M_EXT;
+
     q = (struct ipasfrag *)q->ipf_next;
     while (q != (struct ipasfrag *)&fp->frag_link) {
         struct mbuf *t = dtom(slirp, q);
@@ -348,7 +350,7 @@ insert:
      * the old buffer (in the mbuf), so we must point ip
      * into the new buffer.
      */
-    if (m->m_flags & M_EXT) {
+    if (!was_ext && m->m_flags & M_EXT) {
         int delta = (char *)q - m->m_dat;
         q = (struct ipasfrag *)(m->m_ext + delta);
     }