diff --git a/tools/plan-viewer/README.md b/tools/plan-viewer/README.md
index 334e2c1..6917959 100644
--- a/tools/plan-viewer/README.md
+++ b/tools/plan-viewer/README.md
@@ -9,6 +9,7 @@ Open [`index.html`](index.html) in a browser, then drop a JSON file from [`crate
 Alternatively, you can run the commands below to serve the viewer locally:
 
 ```sh
+make shell # Go into the Nix shells
 make viewer
 ```