diff --git a/reproducibility.bib b/reproducibility.bib
index 997b569..5279e28 100644
--- a/reproducibility.bib
+++ b/reproducibility.bib
@@ -1,2 +1,13 @@
 %% reproducibility.bib
 %% References to work showing reproducibility (or not) in particular areas
+
+@letter{Hooft_Errors_1996,
+  langid = {english},
+  title = {Errors in Protein Structures},
+  url = {https://www.nature.com/articles/381272a0},
+  type = {Comments and Opinion},
+  urldate = {2018-06-15},
+  date = {1996-05-23},
+  author = {Hooft, Rob W. W. and Vriend, Gert and Sander, Chris and Abola, Enrique E.},
+  doi = {10.1038/381272a0}
+}