diff --git a/Gemfile.lock b/Gemfile.lock
index bdaa34c..1c95e18 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -30,12 +30,14 @@ GEM
       rack (>= 2.1, < 4.a)
     hashdiff (1.1.0)
     hashie (5.0.0)
-    icalendar (2.10.2)
+    icalendar (2.10.3)
       ice_cube (~> 0.16)
+      ostruct
     ice_cube (0.17.0)
     mustermann (3.0.0)
       ruby2_keywords (~> 0.0.1)
     nio4r (2.7.3)
+    ostruct (0.6.0)
     parallel (1.26.3)
     public_suffix (5.0.5)
     puma (6.4.3)