diff --git a/cue/objects/utils.py b/cue/objects/utils.py
index 5db09696..e19c32e3 100644
--- a/cue/objects/utils.py
+++ b/cue/objects/utils.py
@@ -123,7 +123,7 @@ def dt_serializer(name):
     """Return a datetime serializer for a named attribute."""
     def serializer(self, name=name):
         if getattr(self, name) is not None:
-            return timeutils.isotime(getattr(self, name))
+            return getattr(self, name).isoformat()
         else:
             return None
     return serializer
@@ -143,4 +143,4 @@ def obj_serializer(name):
             return getattr(self, name).obj_to_primitive()
         else:
             return None
-    return serializer
\ No newline at end of file
+    return serializer