diff --git a/src/includes/LRUCache.h b/src/includes/LRUCache.h
index cf7df30..50467d5 100644
--- a/src/includes/LRUCache.h
+++ b/src/includes/LRUCache.h
@@ -60,7 +60,7 @@ public:
   {
   public:
     bool operator()(const NodeType *a,
-                    const NodeType *b)
+                    const NodeType *b) const
     {
       return a->key < b->key;
     }