diff --git a/lib/digraph.js b/lib/digraph.js
index <HASH>..<HASH> 100644
--- a/lib/digraph.js
+++ b/lib/digraph.js
@@ -106,7 +106,7 @@ Digraph.prototype.predecessors = function(v) {
 Digraph.prototype.neighbors = function(v) {
   var adjs = this._inEdges[v];
   if (adjs) {
-    _.merge(adjs, this._outEdges[v]);
+    _.assign(adjs, this._outEdges[v]);
     return _.keys(adjs);
   }
 };
Replace merge with assign for neighbors

Merge tries to recursively merge objects which has some overhead versus
assign.