diff --git a/paper/paper.bib b/paper/paper.bib
index 8efccb9..d14fe5a 100644
--- a/paper/paper.bib
+++ b/paper/paper.bib
@@ -43,7 +43,8 @@ @book{kans2016entrez
     author={Kans, J.},
     year={2016},
     publisher={National Center for Biotechnology Information},
-    address={Bethesda, MD, USA}
+    address={Bethesda, MD, USA},
+    url={https://www.ncbi.nlm.nih.gov/books/NBK179288/}
     % DOI not found on site
 }