diff --git a/static/js/graphing.js b/static/js/graphing.js
index 18bb09496..60e7d1b33 100644
--- a/static/js/graphing.js
+++ b/static/js/graphing.js
@@ -521,6 +521,11 @@ ImageHistoryTree.prototype.pruneUnreferenced_ = function(node) {
     }
     node.children = surviving_children;
   }
+
+  if (!node.tags) {
+    return node.children.length == 0;
+  }
+
   return (node.children.length == 0 && node.tags.length == 0);
 };