diff --git a/Gemfile.lock b/Gemfile.lock
index d392a8cfd71..e6b5306d702 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -152,7 +152,7 @@ GEM
     loofah (2.0.3)
       nokogiri (>= 1.5.9)
     lru_redux (1.1.0)
-    mail (2.6.5)
+    mail (2.6.6.rc1)
       mime-types (>= 1.16, < 4)
     memory_profiler (0.9.7)
     message_bus (2.0.2)