diff --git a/paper/paper.bib b/paper/paper.bib
index 5378a9c..c0ae588 100644
--- a/paper/paper.bib
+++ b/paper/paper.bib
@@ -219,6 +219,7 @@ @article{Schmitt1998
 	number       = 13,
 	pages        = {2788--2797},
 	doi          = {10.1364/AO.37.002788},
+	issn         = {0003-6935},
 	url          = {http://www.ncbi.nlm.nih.gov/pubmed/18273225},
 	pmid         = 18273225
 }