diff --git a/actionpack/lib/action_view/helpers/asset_tag_helper.rb b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
index c2b4f51c9c..623ed1e8df 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helper.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
@@ -612,7 +612,7 @@ module ActionView
         end
 
         def join_asset_file_contents(paths)
-          paths.collect { |path| File.read(File.join(ASSETS_DIR, path.split("?").first)) }.join("\n\n")
+          paths.collect { |path| File.read(asset_file_path(path)) }.join("\n\n")
         end
 
         def write_asset_file_contents(joined_asset_path, asset_paths)
@@ -621,10 +621,14 @@ module ActionView
 
           # Set mtime to the latest of the combined files to allow for
           # consistent ETag without a shared filesystem.
-          mt = asset_paths.map { |p| File.mtime(File.join(ASSETS_DIR, p)) }.max
+          mt = asset_paths.map { |p| File.mtime(asset_file_path(p)) }.max
           File.utime(mt, mt, joined_asset_path)
         end
 
+        def asset_file_path(path)
+          File.join(ASSETS_DIR, path.split('?').first)
+        end
+
         def collect_asset_files(*path)
           dir = path.first