diff --git a/books/free-programming-books-subjects.md b/books/free-programming-books-subjects.md
index 189e355bb..d525a45cd 100644
--- a/books/free-programming-books-subjects.md
+++ b/books/free-programming-books-subjects.md
@@ -303,7 +303,7 @@ Books that cover a specific programming language can be found in the [BY PROGRAM
 ### Embedded Systems
 
 * [Control and Embedded Systems](http://www.learn-c.com) (HTML)
-* [Discovering the STM32 Microcontroller](http://www.cs.indiana.edu/~geobrown/book.pdf) (PDF)
+* [Discovering the STM32 Microcontroller](http://www.cs.indiana.edu/~geobrown/book.pdf) (PDF) (CC BY-NC-SA 3.0)
 * [First Steps with Embedded Systems](https://www.phaedsys.com/principals/bytecraft/bytecraftdata/bcfirststeps.pdf) - Byte Craft Limited (PDF)
 * [Introduction to Embedded Systems, Second Edition](https://ptolemy.berkeley.edu/books/leeseshia/releases/LeeSeshia_DigitalV2_2.pdf) - Edward Ashford Lee, Sanjit Arunkumar Seshia (PDF)
 * [Introduction to Microcontrollers](http://www.embeddedrelated.com/showarticle/453.php) (HTML)