diff --git a/content/3.defense-systems/pycsar.md b/content/3.defense-systems/pycsar.md
index 0d9ca792062fa8c35443ce9a332194f120897c51..e58810c4e80af7b89c6e3ad7ebdf0f1d2e7863b5 100644
--- a/content/3.defense-systems/pycsar.md
+++ b/content/3.defense-systems/pycsar.md
@@ -59,7 +59,7 @@ Proportion of genome encoding the Pycsar system for the 14 phyla with more than
 ## Structure
 
 ### Experimentaly determined structure
-From :ref{ref=10.1016/j.cell.2021.09.031} in *Burkholderia cepacia* LK29:
+From :ref{doi=10.1016/j.cell.2021.09.031} in *Burkholderia cepacia* LK29:
 
 ::molstar-pdbe-plugin
 ---