diff --git a/_projects/sap.md b/_projects/sap.md
index 787540f..a79a76b 100644
--- a/_projects/sap.md
+++ b/_projects/sap.md
@@ -131,13 +131,15 @@ plt.show()
 ![](/assets/img/sap_2.png){.img-fluid .z-depth-1 .rounded}
 
 
-To go further, please have a look to the [online documentation][doc].
+To go further, please have a look to the [online documentation][doc-api].
 
 
 This package has been used, amongst other projects, to perform an
 experimental comparison of the attribute profiles and their variations
 in a published paper [^1].
 
+[doc-api]: https://python-sap.readthedocs.io/en/master/source/sap.html
+
 [^1]: Deise Santana Maia, Minh-Tan Pham, Erchan Aptoula, Florent
   Guiotte, et Sébastien Lefèvre, « *Classification of Remote Sensing
   Data With Morphological Attribute Profiles: A decade of advances* »,