diff --git a/setup.cfg b/setup.cfg
index 4c0d7d4..f59bac7 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -88,6 +88,8 @@ filterwarnings =
     ignore: invalid value encountered in true_divide
     # https://github.com/pytest-dev/pytest-cov/issues/557
     ignore:The --rsyncdir command line argument and rsyncdirs config variable are deprecated.:DeprecationWarning
+doctest_subpackage_requires =
+    docs/* = ndcube<2.3.0
 
 [pycodestyle]
 max_line_length = 120