diff --git a/docs/contributing/how-to-add-class-documentation.md b/docs/contributing/how-to-add-class-documentation.md
index e1ba10231a..12779e9901 100644
--- a/docs/contributing/how-to-add-class-documentation.md
+++ b/docs/contributing/how-to-add-class-documentation.md
@@ -33,8 +33,9 @@ which are implementation details.
 Running Doxygen
 ---------------
 
-First, make sure you have a recent version of Doxygen installed in your system
-(currently Doxygen 1.8.8 is used).
+First, make sure you have a recent version of Doxygen (currently Doxygen 1.8.8
+is used) and Graphviz installed in your system (under Windows Graphviz
+location should be in %PATH%).
 
 On Unix: