1 files changed, 5 insertions, 2 deletions
diff --git a/actionpack/lib/action_view/helpers/asset_tag_helpers/stylesheet_tag_helpers.rb b/actionpack/lib/action_view/helpers/asset_tag_helpers/stylesheet_tag_helpers.rb
index d02b28d7f6..f3e041de95 100644
--- a/actionpack/lib/action_view/helpers/asset_tag_helpers/stylesheet_tag_helpers.rb
+++ b/actionpack/lib/action_view/helpers/asset_tag_helpers/stylesheet_tag_helpers.rb
@@ -44,7 +44,10 @@ module ActionView
           #     <link href="/stylesheets/body.css"  media="screen" rel="stylesheet" type="text/css" />
           #     <link href="/stylesheets/tail.css"  media="screen" rel="stylesheet" type="text/css" />
           def register_stylesheet_expansion(expansions)
-            StylesheetIncludeTag.expansions.merge!(expansions)
+            style_expansions = StylesheetIncludeTag.expansions
+            expansions.each do |key, values|
+              style_expansions[key] = (style_expansions[key] || []) | Array(values) if values
+            end
           end
         end
 
@@ -141,4 +144,4 @@ module ActionView
 
     end
   end
-end
-\ No newline at end of file
+end