diff --git a/test-files/fixes/duplicates/before.bib b/test-files/fixes/duplicates/before.bib
index b48a110..804437e 100644
--- a/test-files/fixes/duplicates/before.bib
+++ b/test-files/fixes/duplicates/before.bib
@@ -4,6 +4,7 @@ @book{knuth1974
   publisher = {Addison-Wesley Professional},
   title = {The TeX Book},
   year = {1984},
+  month = {January}
 }
 
 @book{knuth1974,