diff --git a/nix/tests/module.nix b/nix/tests/module.nix
index 1a53a53..b3de3b3 100644
--- a/nix/tests/module.nix
+++ b/nix/tests/module.nix
@@ -81,5 +81,11 @@ pkgs.runCommand "tide-module-test" { } ''
   ${pkgs.gnugrep}/bin/grep -F \
     "https://chat.whatsapp.com/FLdSwkdiChA9wvXxooUV9K" \
     ${landingPage}/index.html
+  if ${pkgs.gnugrep}/bin/grep -F \
+    'class="button button--small"' \
+    ${landingPage}/index.html; then
+    echo "unexpected small button in landing-page header" >&2
+    exit 1
+  fi
   touch "$out"
 ''