diff --git a/pkgs/by-name/ma/mainsail/package.nix b/pkgs/by-name/ma/mainsail/package.nix
index b9d6961fc1f9..2118f7775d5a 100644
--- a/pkgs/by-name/ma/mainsail/package.nix
+++ b/pkgs/by-name/ma/mainsail/package.nix
@@ -21,7 +21,7 @@ buildNpmPackage rec {
   nodejs = nodejs_20;
 
   # Prevent Cypress binary download.
-  CYPRESS_INSTALL_BINARY = 0;
+  env.CYPRESS_INSTALL_BINARY = 0;
 
   preConfigure = ''
     # Make the build.zip target do nothing, since we will just copy these files later.