diff --git a/lib/white_list_filter.rb b/lib/white_list_filter.rb
index 5c2d29f..8218ba1 100644
--- a/lib/white_list_filter.rb
+++ b/lib/white_list_filter.rb
@@ -9,7 +9,7 @@ module WhiteListFilter
       unless iframe =~ /src=['"].*src=['"]/
         trusted_sites.each do |trusted_site|
           re_dom = trusted_site.gsub('.', '\.')
-          if iframe =~ /src=["']https?:\/\/(www\.)?#{re_dom}\//
+          if iframe =~ /src=["'](https?:)?\/\/(www\.)?#{re_dom}\//
             result = iframe
           end
         end
diff --git a/test/unit/white_list_filter_test.rb b/test/unit/white_list_filter_test.rb
index 8b7e0d9..27d6d29 100644
--- a/test/unit/white_list_filter_test.rb
+++ b/test/unit/white_list_filter_test.rb
@@ -40,6 +40,15 @@ class WhiteListFilterTest < ActiveSupport::TestCase
     assert_equal "<iframe src='http://avideosite.com/videos.ogg'></iframe>", check_iframe_on_content(content, environment.trusted_sites_for_iframe)
   end
 
+  should 'allow iframe if it is from a trusted site and protocol was not specified' do
+    env = Environment.default
+    env.trusted_sites_for_iframe = ['avideosite.com']
+    env.save
+    assert_includes Environment.default.trusted_sites_for_iframe, 'avideosite.com'
+    content = "<iframe src='//avideosite.com/videos.ogg'></iframe>"
+    assert_equal "<iframe src='//avideosite.com/videos.ogg'></iframe>", check_iframe_on_content(content, environment.trusted_sites_for_iframe)
+  end
+
   should 'remove only the iframe from untrusted site' do
     content = "<iframe src='http://stream.softwarelivre.org/videos.ogg'></iframe><iframe src='http://untrusted_site.com/videos.ogg'></iframe>"
     assert_equal "<iframe src='http://stream.softwarelivre.org/videos.ogg'></iframe>", check_iframe_on_content(content, environment.trusted_sites_for_iframe)
--
libgit2 0.21.2