diff --git a/book.json b/book.json
index bd633af..cc75017 100644
--- a/book.json
+++ b/book.json
@@ -252,7 +252,7 @@
                         "https://softwareengineeringdaily.com/2015/07/27/react-js-with-sebastian-markbage-and-christopher-chedeau/"
                 ],
                 "chen09": [
-                        "Chien-Tsun Chen, Yu Chin Cheng, Chin-Yun Hsieh, and I-Lang Wu", 
+                        "Chien-Tsun Chen, Yu Chin Cheng, Chin-Yun Hsieh, and I-Lang Wu", 2008,
                         "Exception handling refactorings: Directed by goals and driven by bug fixing", "Journal of Systems and Software", 
                         "https://doi.org/10.1016/j.jss.2008.06.035"
                 ],