diff --git a/pykeepass/baseelement.py b/pykeepass/baseelement.py
index 6e4e96f0..2ca238fa 100644
--- a/pykeepass/baseelement.py
+++ b/pykeepass/baseelement.py
@@ -19,7 +19,7 @@ def __init__(self, element, kp=None, icon=None, expires=False,
             self._element.append(E.IconID(icon))
         current_time_str = self._kp._encode_time(datetime.now(timezone.utc))
         if expiry_time:
-            expiry_time_str = self._kp._encode_time(expiry_time)
+            expiry_time_str = self._kp._encode_time(expiry_time.astimezone(timezone.utc))
         else:
             expiry_time_str = current_time_str
 
diff --git a/pykeepass/pykeepass.py b/pykeepass/pykeepass.py
index f0131c1c..93eb71e9 100644
--- a/pykeepass/pykeepass.py
+++ b/pykeepass/pykeepass.py
@@ -28,7 +28,7 @@
 BLANK_DATABASE_FILENAME = "blank_database.kdbx"
 BLANK_DATABASE_LOCATION = os.path.join(os.path.dirname(os.path.realpath(__file__)), BLANK_DATABASE_FILENAME)
 BLANK_DATABASE_PASSWORD = "password"
-DT_ISOFORMAT = "%Y-%m-%dT%H:%M:%S%z"
+DT_ISOFORMAT = "%Y-%m-%dT%H:%M:%S%fZ"
 
 class PyKeePass():
     """Open a KeePass database
@@ -795,7 +795,7 @@ def _encode_time(self, value):
                 struct.pack('<Q', diff_seconds)
             ).decode('utf-8')
         else:
-            return value.isoformat()
+            return value.strftime(DT_ISOFORMAT)
 
     def _decode_time(self, text):
         """datetime.datetime: Convert base64 time or plaintext time to datetime"""
@@ -810,9 +810,9 @@ def _decode_time(self, text):
                     )
                 )
             except BinasciiError:
-                return datetime.strptime(text, DT_ISOFORMAT).astimezone(timezone.utc)
+                return datetime.strptime(text, DT_ISOFORMAT).replace(tzinfo=timezone.utc)
         else:
-            return datetime.strptime(text, DT_ISOFORMAT).astimezone(timezone.utc)
+            return datetime.strptime(text, DT_ISOFORMAT).replace(tzinfo=timezone.utc)
 
 def create_database(
         filename, password=None, keyfile=None, transformed_key=None