diff --git a/notebooks/shared/fuzzingbook.bib b/notebooks/shared/fuzzingbook.bib
index 3c009188..303a6d64 100644
--- a/notebooks/shared/fuzzingbook.bib
+++ b/notebooks/shared/fuzzingbook.bib
@@ -949,7 +949,7 @@ @article{Ernst2001
  publisher = {IEEE Press},
  address = {Piscataway, NJ, USA},
  keywords = {Program invariants, formal specification, software evolution, dynamic analysis, execution traces, logical inference, pattern recognition.},
- url = {https://homes.cs.washington.edu/~mernst/pubs/invariants-tse2001.pdf}
+ EXTRAurl = {https://homes.cs.washington.edu/~mernst/pubs/invariants-tse2001.pdf}
 } 
 
 @inproceedings{Pacheco2005,
@@ -967,7 +967,7 @@ @inproceedings{Pacheco2005
  acmid = {2144921},
  publisher = {Springer-Verlag},
  address = {Berlin, Heidelberg},
- url = {https://homes.cs.washington.edu/~mernst/pubs/classify-tests-ecoop2005.pdf}
+ EXTRAurl = {https://homes.cs.washington.edu/~mernst/pubs/classify-tests-ecoop2005.pdf}
 }
 
 @inproceedings{Ammons2002,