diff --git a/actionpack/lib/action_view/helpers/asset_tag_helper.rb b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
index 8731ed0..3b0768a 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helper.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helper.rb
@@ -620,7 +620,7 @@ module ActionView
options.symbolize_keys!
src = options[:src] = path_to_image(source)
- options[:alt] ||= File.basename(src, '.*').capitalize
+ options[:alt] = options.fetch(:alt){ File.basename(src, '.*').capitalize }
if size = options.delete(:size)
options[:width], options[:height] = size.split("x") if size =~ %r{^\d+x\d+$}
diff --git a/actionpack/test/template/asset_tag_helper_test.rb b/actionpack/test/template/asset_tag_helper_test.rb
index 124bf73..b6a6f52 100644
--- a/actionpack/test/template/asset_tag_helper_test.rb
+++ b/actionpack/test/template/asset_tag_helper_test.rb
@@ -154,7 +154,8 @@ class AssetTagHelperTest < ActionView::TestCase
%(image_tag(".pdf.png")) => %(),
%(image_tag("http://www.rubyonrails.com/images/rails.png")) => %(),
%(image_tag("mouse.png", :mouseover => "/images/mouse_over.png")) => %(),
- %(image_tag("mouse.png", :mouseover => image_path("mouse_over.png"))) => %()
+ %(image_tag("mouse.png", :mouseover => image_path("mouse_over.png"))) => %(),
+ %(image_tag("mouse.png", :alt => nil)) => %()
}
FaviconLinkToTag = {