diff --git a/content/activities/201405-codebreakers-1.md b/content/activities/201405-codebreakers-1.md
index c53d1cd8..a427999f 100644
--- a/content/activities/201405-codebreakers-1.md
+++ b/content/activities/201405-codebreakers-1.md
@@ -1,6 +1,6 @@
 ---
 kind: event
-startdate: 2014-05-16T18:00:00
+startdate: 2014-05-16T18:00:00Z
 duration: 180m
 title: "Workshop: Codebreakers (Teil 1)"
 speakers:
diff --git a/content/activities/201406-codebreakers-2.md b/content/activities/201406-codebreakers-2.md
index 4b18ba9b..41e1c49b 100644
--- a/content/activities/201406-codebreakers-2.md
+++ b/content/activities/201406-codebreakers-2.md
@@ -1,6 +1,6 @@
 ---
 kind: event
-startdate: 2014-06-06T18:00:00
+startdate: 2014-06-06T18:00:00Z
 duration: 180m
 title: "Workshop: Codebreakers (Teil 2)"
 speakers:
diff --git a/content/activities/201406-codebreakers-3.md b/content/activities/201406-codebreakers-3.md
index 7825064e..70547690 100644
--- a/content/activities/201406-codebreakers-3.md
+++ b/content/activities/201406-codebreakers-3.md
@@ -1,6 +1,6 @@
 ---
 kind: event
-startdate: 2014-06-20T18:00:00
+startdate: 2014-06-20T18:00:00Z
 duration: 180m
 title: "Workshop: Codebreakers (Teil 3)"
 speakers: