diff --git a/examples/persistence/kdtree/Gemfile.lock b/examples/persistence/kdtree/Gemfile.lock
index b0ef7eb6e..4c004982c 100644
--- a/examples/persistence/kdtree/Gemfile.lock
+++ b/examples/persistence/kdtree/Gemfile.lock
@@ -5,7 +5,7 @@ GEM
     minitest (2.5.0)
     mustermann (1.1.1)
       ruby2_keywords (~> 0.0.1)
-    rack (2.2.3.1)
+    rack (2.2.6.4)
     rack-protection (2.2.0)
       rack
     ruby2_keywords (0.0.5)