diff --git a/isisd/isis_pdu.c b/isisd/isis_pdu.c
index 8d8a5e0..166dd7c 100644
--- a/isisd/isis_pdu.c
+++ b/isisd/isis_pdu.c
@@ -566,6 +566,17 @@
    * the circuit
    */
   adj = circuit->u.p2p.neighbor;
+  /* If an adjacency exists, check it is with the source of the hello
+   * packets */
+  if (adj)
+    {
+      if (memcmp(hdr->source_id, adj->sysid, ISIS_SYS_ID_LEN))
+	{
+          zlog_debug("hello source and adjacency do not match, set adj down\n");
+          isis_adj_state_change (adj, ISIS_ADJ_DOWN, "adj do not exist");
+          return 0;
+        }
+    }
   if (!adj || adj->level != hdr->circuit_t)
     {
       if (!adj)