diff --git a/qa/workunits/mon/crush_ops.sh b/qa/workunits/mon/crush_ops.sh
index 6c13b699081..aa287c79ce3 100755
--- a/qa/workunits/mon/crush_ops.sh
+++ b/qa/workunits/mon/crush_ops.sh
@@ -213,4 +213,15 @@ ceph osd pool rm cool cool --yes-i-really-really-mean-it
 ceph osd pool rm cold cold --yes-i-really-really-mean-it
 ceph osd crush weight-set rm-compat
 
+# weight set vs device classes vs move
+ceph osd crush weight-set create-compat
+ceph osd crush add-bucket fooo host
+ceph osd crush move fooo root=default
+ceph osd crush add-bucket barr rack
+ceph osd crush move barr root=default
+ceph osd crush move fooo rack=barr
+ceph osd crush rm fooo
+ceph osd crush rm barr
+ceph osd crush weight-set rm-compat
+
 echo OK
diff --git a/src/crush/CrushWrapper.cc b/src/crush/CrushWrapper.cc
index 5b5d21a2ec5..c5be8357137 100644
--- a/src/crush/CrushWrapper.cc
+++ b/src/crush/CrushWrapper.cc
@@ -1573,7 +1573,7 @@ int CrushWrapper::populate_classes(
   // accumulate weight values for each carg and bucket as we go. because it is
   // depth first, we will have the nested bucket weights we need when we
   // finish constructing the containing buckets.
-  map<int,map<int,vector<int>>> cmap_item_weight; // cargs -> bno -> weights
+  map<int,map<int,vector<int>>> cmap_item_weight; // cargs -> bno -> [bucket weight for each position]
   set<int> roots;
   find_nonshadow_roots(&roots);
   for (auto &r : roots) {
@@ -2182,8 +2182,10 @@ int CrushWrapper::device_class_clone(
 	int item = copy->items[i];
 	if (item >= 0) {
 	  n.weight_set[s].weights[i] = o.weight_set[s].weights[item_orig_pos[i]];
-	} else {
+	} else if ((*cmap_item_weight)[w.first].count(item)) {
 	  n.weight_set[s].weights[i] = (*cmap_item_weight)[w.first][item][s];
+	} else {
+	  n.weight_set[s].weights[i] = 0;
 	}
 	bucket_weights[s] += n.weight_set[s].weights[i];
       }