diff --git a/src/libnm-glib-aux/nm-prioq.c b/src/libnm-glib-aux/nm-prioq.c
index c53e74fc1c..897d65dd51 100644
--- a/src/libnm-glib-aux/nm-prioq.c
+++ b/src/libnm-glib-aux/nm-prioq.c
@@ -288,14 +288,28 @@ find_item(NMPrioq *q, void *data, unsigned *idx)
         return NULL;
     }
 
+    /* If the user however provides an "idx" pointer, then we assert that it is
+     * consistent. That is, if data is not in the queue, then we require that
+     * "*idx" is NM_PRIOQ_IDX_NULL, and otherwise we require that we really
+     * find "data" at index "*idx".
+     *
+     * This means, when the user calls nm_prioq_{remove,update,reshuffle}()
+     * with an "idx", then they must make sure that the index is consistent.
+     * Usually this means they are required to initialize the index to
+     * NM_PRIOQ_IDX_NULL while the data is not in the heap.
+     *
+     * This is done to assert more, and requires a stricter usage of the API
+     * (in the hope to find misuses of the index). */
+
     if (*idx >= q->_priv.n_items) {
+        nm_assert(*idx == NM_PRIOQ_IDX_NULL);
         return NULL;
     }
 
     i = &q->_priv.items[*idx];
 
     if (i->data != data)
-        return NULL;
+        return nm_assert_unreachable_val(NULL);
 
     return i;
 }
diff --git a/src/libnm-lldp/nm-lldp-neighbor.c b/src/libnm-lldp/nm-lldp-neighbor.c
index f1e2d42eb0..a2a9695e85 100644
--- a/src/libnm-lldp/nm-lldp-neighbor.c
+++ b/src/libnm-lldp/nm-lldp-neighbor.c
@@ -735,6 +735,7 @@ nm_lldp_neighbor_new(size_t raw_size)
 
     n->raw_size  = raw_size;
     n->ref_count = 1;
+    n->prioq_idx = NM_PRIOQ_IDX_NULL;
     return n;
 }