diff --git a/app/controllers/api/v1/release_engines/npm/package_metadata_controller.rb b/app/controllers/api/v1/release_engines/npm/package_metadata_controller.rb
index 6e939c180..537ffd80b 100644
--- a/app/controllers/api/v1/release_engines/npm/package_metadata_controller.rb
+++ b/app/controllers/api/v1/release_engines/npm/package_metadata_controller.rb
@@ -20,7 +20,7 @@ def show
         to: :index?
 
       # FIXME(ezekg) https://github.com/brianhempel/active_record_union/issues/35
-      last_modified = artifacts.maximum(:"#{artifacts.table_name}.updated_at")
+      last_modified = artifacts.collect(&:updated_at).max
       latest        = artifacts.first
       metadata      = artifacts.reduce(
         name: package.key,
diff --git a/app/controllers/api/v1/release_engines/pypi/simple_controller.rb b/app/controllers/api/v1/release_engines/pypi/simple_controller.rb
index a701b5720..6fd462f8d 100644
--- a/app/controllers/api/v1/release_engines/pypi/simple_controller.rb
+++ b/app/controllers/api/v1/release_engines/pypi/simple_controller.rb
@@ -33,7 +33,7 @@ def show
         to: :index?
 
       # FIXME(ezekg) https://github.com/brianhempel/active_record_union/issues/35
-      last_modified = artifacts.maximum(:"#{artifacts.table_name}.updated_at")
+      last_modified = artifacts.collect(&:updated_at).max
       return unless
         stale?(artifacts, last_modified:, cache_control: { max_age: 1.day, private: true })