diff --git a/sys/net/debugnet.c b/sys/net/debugnet.c
--- a/sys/net/debugnet.c
+++ b/sys/net/debugnet.c
@@ -605,8 +605,8 @@
 {
 	struct ifnet *ifp;
 
-	MPASS(g_debugnet_pcb_inuse);
 	MPASS(pcb == &g_dnet_pcb);
+	MPASS(pcb->dp_drv_input == NULL || g_debugnet_pcb_inuse);
 
 	ifp = pcb->dp_ifp;
 	if (ifp != NULL) {
@@ -646,6 +646,7 @@
 		.dp_seqno = 1,
 		.dp_ifp = dcp->dc_ifp,
 		.dp_rx_handler = dcp->dc_rx_handler,
+		.dp_drv_input = NULL,
 	};
 
 	/* Switch to the debugnet mbuf zones. */