diff --git a/ospfd/ospf_flood.c b/ospfd/ospf_flood.c
index 41661da..fc0bbf1 100644
--- a/ospfd/ospf_flood.c
+++ b/ospfd/ospf_flood.c
@@ -319,7 +319,8 @@
      procedure cannot overwrite the newly installed LSA until
      MinLSArrival seconds have elapsed. */  
 
-  new = ospf_lsa_install (ospf, nbr->oi, new);
+  if (! (new = ospf_lsa_install (ospf, nbr->oi, new)))
+    return 0; /* unknown LSA type */
 
   /* Acknowledge the receipt of the LSA by sending a Link State
      Acknowledgment packet back out the receiving interface. */