diff --git a/config/initializers/tenanting.rb b/config/initializers/tenanting.rb
index 25833f42e..5ada06981 100644
--- a/config/initializers/tenanting.rb
+++ b/config/initializers/tenanting.rb
@@ -1,9 +1,11 @@
 Rails.application.config.after_initialize do
+  # in production, we're using a two-level subdomain like "tenant.fizzy.37signals.com", but in
+  # development and beta it's only a single-level subdomain.
   Rails.application.config.active_record_tenanted.tenant_resolver = ->(request) do
-    # in production, we're using a two-level subdomain like "tenant.fizzy.37signals.com", but in
-    # development and beta it's only a single-level subdomain.
+    next nil if request.path == "/up"
+
     tld_length = request.domain == "37signals.com" ? 2 : 1
-    request.subdomain(tld_length).presence # || "no-such-tenant-exists" # this is a quick fix for now
+    request.subdomain(tld_length).presence || "return-404" # this is a quick fix for now
   end
 end