diff --git a/sys/dev/usb/umidi.c b/sys/dev/usb/umidi.c
index 6f8f8397e144..7cfa6ea8e644 100644
--- a/sys/dev/usb/umidi.c
+++ b/sys/dev/usb/umidi.c
@@ -727,8 +727,14 @@ alloc_all_endpoints(struct umidi_softc *sc)
 	for (i = sc->sc_out_num_endpoints+sc->sc_in_num_endpoints; i > 0; i--) {
 		err = alloc_pipe(ep++);
 		if (err != USBD_NORMAL_COMPLETION) {
-			for (; ep != sc->sc_endpoints; ep--)
+			for (; ep != sc->sc_endpoints; ep--) {
+				KASSERTMSG(ep[-1].pipe != NULL,
+				    "i=%d nin=%d nout=%d",
+				    (int)(ep - 1 - sc->sc_endpoints),
+				    sc->sc_in_num_endpoints,
+				    sc->sc_out_num_endpoints);
 				free_pipe(ep-1);
+			}
 			kmem_free(sc->sc_endpoints, sc->sc_endpoints_len);
 			sc->sc_endpoints = sc->sc_out_ep = sc->sc_in_ep = NULL;
 			break;
@@ -747,8 +753,12 @@ free_all_endpoints(struct umidi_softc *sc)
 		return;
 	}
 
-	for (i=0; i<sc->sc_in_num_endpoints+sc->sc_out_num_endpoints; i++)
+	for (i=0; i<sc->sc_in_num_endpoints+sc->sc_out_num_endpoints; i++) {
+		KASSERTMSG(sc->sc_endpoints[i].pipe != NULL,
+		    "i=%d nin=%d nout=%d",
+		    i, sc->sc_in_num_endpoints, sc->sc_out_num_endpoints);
 		free_pipe(&sc->sc_endpoints[i]);
+	}
 	kmem_free(sc->sc_endpoints, sc->sc_endpoints_len);
 	sc->sc_endpoints = sc->sc_out_ep = sc->sc_in_ep = NULL;
 }