diff --git a/books/free-programming-books.md b/books/free-programming-books.md
index c9b844ac0..1c1a63051 100644
--- a/books/free-programming-books.md
+++ b/books/free-programming-books.md
@@ -1460,7 +1460,7 @@ Kerridge (PDF) (email address *requested*, not required)
 
 ### Fortran
 
-* [Professional Programmer’s Guide to Fortran77](https://www.star.le.ac.uk/~cgp/prof77.pdf) (PDF)
+* [Professional Programmer’s Guide to Fortran77 (2005)](https://www.star.le.ac.uk/~cgp/prof77.pdf) (PDF)
 * [Self Study Guide: Programming in Fortran 95](http://www.mrao.cam.ac.uk/~rachael/compphys/SelfStudyF95.pdf) (PDF)