diff --git a/README.md b/README.md
index d072278b25f79bf3d11f5a671902ba2f4618572e..cc4f59263b8b14c61106d0ea44f88a73b7479137 100644
--- a/README.md
+++ b/README.md
@@ -47,7 +47,7 @@ cd ../corsika-install
 share/examples/cascade_example
 ```
 
-Visualize output: 
+Visualize output (needs gnuplot installed): 
 ```
 bash share/tools/plot_tracks.sh tracks.dat 
 firefox tracks.dat.gif