diff --git a/README.md b/README.md
index e0f163c..fd5c6cc 100644
--- a/README.md
+++ b/README.md
@@ -3,6 +3,7 @@ Simulate X-ray with CERN tools.
 ### Prerequisites
 * Linux or MacOS (Tested on Ubuntu 16.04, MacOS High Sierra 10.13.3 and Linux Subsystem for Windows 10)
 * CERN Geant4
+* CERN Root (Tested with 6.13/3)
 * CMake
 
 ### Building