diff --git a/lib/jekyll/cloudinary.rb b/lib/jekyll/cloudinary.rb
index 8f6b1d1..dc323a4 100644
--- a/lib/jekyll/cloudinary.rb
+++ b/lib/jekyll/cloudinary.rb
@@ -178,7 +178,7 @@ def render(context)
         end
 
         # alt and title attributes should go only to the <img> even when there is a caption
-        img_attr = ""
+        img_attr = "".dup
         if html_attr["alt"]
           img_attr << " alt=\"#{html_attr["alt"]}\""
           html_attr.delete("alt")