diff --git a/slirp/ip_input.c b/slirp/ip_input.c
index e7f275613f..505149a33e 100644
--- a/slirp/ip_input.c
+++ b/slirp/ip_input.c
@@ -392,8 +392,7 @@ insert:
 	 * into the new buffer.
 	 */
 	if (m->m_flags & M_EXT) {
-	  int delta;
-	  delta = (char *)ip - m->m_dat;
+	  int delta = (char *)q - m->m_dat;
 	  q = (struct ipasfrag *)(m->m_ext + delta);
 	}