diff --git a/src/Hakyll/Web/Html.hs b/src/Hakyll/Web/Html.hs
index bed7755..6b7ec88 100644
--- a/src/Hakyll/Web/Html.hs
+++ b/src/Hakyll/Web/Html.hs
@@ -55,7 +55,7 @@ demoteHeaders = withTags $ \tag -> case tag of
--------------------------------------------------------------------------------
isUrlAttribute :: String -> Bool
-isUrlAttribute = (`elem` ["src", "href", "data"])
+isUrlAttribute = (`elem` ["src", "href", "data", "poster"])
--------------------------------------------------------------------------------
diff --git a/tests/Hakyll/Web/Html/RelativizeUrls/Tests.hs b/tests/Hakyll/Web/Html/RelativizeUrls/Tests.hs
index 7799217..4d9421e 100644
--- a/tests/Hakyll/Web/Html/RelativizeUrls/Tests.hs
+++ b/tests/Hakyll/Web/Html/RelativizeUrls/Tests.hs
@@ -22,6 +22,9 @@ tests = testGroup "Hakyll.Web.Html.RelativizeUrls.Tests" $
relativizeUrlsWith ".." "bar"
, "" @=?
relativizeUrlsWith "../.." ""
+ , "" @=?
+ relativizeUrlsWith "../.."
+ ""
, "Haskell" @=?
relativizeUrlsWith "../.."
"Haskell"