diff --git a/doc/source/index.rst b/doc/source/index.rst
index d5d94ad..fb8c3a3 100644
--- a/doc/source/index.rst
+++ b/doc/source/index.rst
@@ -57,5 +57,5 @@ Indices and tables
 Citation
 ******************
 
-* Please cite `acstools <https://ui.adsabs.harvard.edu/abs/2020ascl.soft11024L/abstract>` if you have used it in your work. 
+* Please cite `acstools <https://ui.adsabs.harvard.edu/abs/2020ascl.soft11024L/abstract>`_ if you have used it in your work.