diff --git a/cert_tools/helpers.py b/cert_tools/helpers.py
index 54af5ea..916939b 100644
--- a/cert_tools/helpers.py
+++ b/cert_tools/helpers.py
@@ -57,5 +57,5 @@ def encode(num, alphabet=BASE62):
 
 
 def create_iso8601_tz():
-    ret = datetime.now(timezone.utc)
+    ret = datetime.now(timezone.utc).isoformat()[:-13]+'Z'
     return ret.isoformat()
\ No newline at end of file