diff --git a/sys/net/dummynet/ip_dummynet.c b/sys/net/dummynet/ip_dummynet.c
--- a/sys/net/dummynet/ip_dummynet.c
+++ b/sys/net/dummynet/ip_dummynet.c
@@ -1366,6 +1366,8 @@
     			    M_DUMMYNET, M_WAITOK);
 
     /* Fill the lookup table with (1 - w_q)^x */
+    if (ioc_fs->lookup_step == 0)
+	return EINVAL;
     x->lookup_step = ioc_fs->lookup_step;
     x->lookup_weight = ioc_fs->lookup_weight;