diff --git a/books/free-programming-books-langs.md b/books/free-programming-books-langs.md
index af1b3c2d4..95edc3bb7 100644
--- a/books/free-programming-books-langs.md
+++ b/books/free-programming-books-langs.md
@@ -546,7 +546,7 @@ Books on general-purpose programming that don't focus on a specific language are
 * [Matters Computational: Ideas, Algorithms, Source Code](http://www.jjj.de/fxt/fxtbook.pdf) - Jorg Arndt (PDF)
 * [Modern C++ Tutorial: C++11/14/17/20 On the Fly](https://www.changkun.de/modern-cpp/pdf/modern-cpp-tutorial-en-us.pdf) - Changkun Ou (PDF) (CC BY-NC-ND)
 * [More C++ Idioms](https://en.wikibooks.org/wiki/More_C%2B%2B_Idioms) - Sumant Tambe, et al. (WikiBooks)
-* [Open Data Structures (In C++)](http://opendatastructures.org/ods-cpp.pdf) - Pat Morin (PDF)
+* [Open Data Structures (In C++)](http://opendatastructures.org/ods-cpp.pdf) - Pat Morin (PDF) (CC BY)
 * [Programming Fundamentals - A Modular Structured Approach using C++](https://archive.org/details/cnx-org-col10621/mode/1up) - Kenneth Leroy Busbee (PDF)
 * [Software Design Using C++](http://cis.stvincent.edu/html/tutorials/swd/) - Br. David Carlson, Br. Isidore Minerd
 * [Software optimization resources](http://www.agner.org/optimize/) - Agner Fog