Index: sys/x86/xen/xen_intr.c
===================================================================
--- sys/x86/xen/xen_intr.c
+++ sys/x86/xen/xen_intr.c
@@ -319,15 +319,15 @@
 	vector = first_evtchn_irq + xen_intr_auto_vector_count;
 	xen_intr_auto_vector_count++;
 
-	KASSERT((intr_lookup_source(vector) == NULL),
-	    ("Trying to use an already allocated vector"));
-
 	mtx_unlock(&xen_intr_isrc_lock);
 	isrc = malloc(sizeof(*isrc), M_XENINTR, M_WAITOK | M_ZERO);
 	isrc->xi_intsrc.is_pic = &xen_intr_pic;
 	isrc->xi_vector = vector;
 	isrc->xi_type = type;
-	intr_register_source(&isrc->xi_intsrc);
+	if (intr_register_source(&isrc->xi_intsrc) != 0) {
+		free(isrc, M_XENINTR);
+		return (NULL);
+	}
 	mtx_lock(&xen_intr_isrc_lock);
 
 	return (isrc);