diff --git a/docs/harness/README.md b/docs/harness/README.md
index 09f0b01..7c32303 100644
--- a/docs/harness/README.md
+++ b/docs/harness/README.md
@@ -5,7 +5,7 @@ This is how to build the diagram from YAML source with wireviz.
 Thusly
 
 ```
-sudo apt install python3-virtualenv python3-pip
+sudo apt install python3-virtualenv python3-pip graphviz
 
 git clone https://github.com/formatc1702/WireViz
 cd WireViz