diff --git a/extras/markdowner.rb b/extras/markdowner.rb
index 7af5fe3..901e3e3 100644
--- a/extras/markdowner.rb
+++ b/extras/markdowner.rb
@@ -27,7 +27,7 @@ class Markdowner
 
     # make links have rel=nofollow
     ng.css("a").each do |h|
-      h[:rel] = "nofollow" unless h[:href].starts_with?("/")
+      h[:rel] = "nofollow" unless URI.parse(h[:href]).host.nil?
     end
 
     ng.at_css("body").inner_html
diff --git a/spec/models/markdowner_spec.rb b/spec/models/markdowner_spec.rb
index 96d66b8..81776c6 100644
--- a/spec/models/markdowner_spec.rb
+++ b/spec/models/markdowner_spec.rb
@@ -35,4 +35,17 @@ describe Markdowner do
       "<p>hi <a href=\"http://example.com/@blahblah/\" rel=\"nofollow\">" <<
         "test</a></p>"
   end
+
+  it "correctly adds nofollow" do
+    Markdowner.to_html("[ex](http://example.com)").should ==
+      "<p><a href=\"http://example.com\" rel=\"nofollow\">" <<
+        "ex</a></p>"
+
+    Markdowner.to_html("[ex](//example.com)").should ==
+      "<p><a href=\"//example.com\" rel=\"nofollow\">" <<
+        "ex</a></p>"
+
+    Markdowner.to_html("[ex](/u/abc)").should ==
+      "<p><a href=\"/u/abc\">ex</a></p>"
+  end
 end