diff --git a/graphicle/data.py b/graphicle/data.py
index c5f183c..abd9f71 100644
--- a/graphicle/data.py
+++ b/graphicle/data.py
@@ -938,7 +938,7 @@ def flatten(
             the aggregation operation over any ``MaskGroup``.
             ``leaves`` brings the innermosted nested ``MaskArray``
             instances to the top level, discarding the rest.
-            Default is``'rise'``.
+            Default is ``rise``.
 
         Returns
         -------