diff --git a/shell.nix b/shell.nix
index 3dc7587..967c1a5 100644
--- a/shell.nix
+++ b/shell.nix
@@ -9,6 +9,7 @@ mkShell {
     ripgrep
     mavenJdk11
     nodejs-14_x
+    which # required by Vaadin
     python3
   ];
 }