diff --git a/plugins/octopress_filters.rb b/plugins/octopress_filters.rb
index 9c7fa6c..48413a8 100644
--- a/plugins/octopress_filters.rb
+++ b/plugins/octopress_filters.rb
@@ -85,7 +85,7 @@ module OctopressLiquidFilters
   # Replaces relative urls with full urls
   def expand_urls(input, url='')
     url ||= '/'
-    input.gsub /(\s+(href|src)\s*=\s*["|']{1})(\/[^\/>]{1}[^\"'>]*)/ do
+    input.gsub /(\s+(href|src|poster)\s*=\s*["|']{1})(\/[^\/>]{1}[^\"'>]*)/ do
       $1+url+$3
     end
   end