diff --git a/lib/oneboxer/base_onebox.rb b/lib/oneboxer/base_onebox.rb
index c855bc21d..1f25b703d 100644
--- a/lib/oneboxer/base_onebox.rb
+++ b/lib/oneboxer/base_onebox.rb
@@ -37,6 +37,11 @@ module Oneboxer
         var.gsub! /https?:\/\//, '//' if var.is_a? String
       end
 
+      # Add wmode=opaque to the iframe src URL so that the flash player is rendered within the document flow instead of on top
+      def append_embed_wmode(var)
+        var.gsub! /(src="[^"]+)/, '\1&wmode=opaque"' if var.is_a? String
+      end
+
     end
 
     def initialize(url, opts={})
diff --git a/lib/oneboxer/flash_video_onebox.rb b/lib/oneboxer/flash_video_onebox.rb
index 96555b1d7..18719409a 100644
--- a/lib/oneboxer/flash_video_onebox.rb
+++ b/lib/oneboxer/flash_video_onebox.rb
@@ -2,12 +2,12 @@ require_dependency 'oneboxer/base_onebox'
 
 module Oneboxer
   class FlashVideoOnebox < BaseOnebox
-    
+
     matcher /^https?:\/\/.*\.(swf|flv)$/
 
     def onebox
       if SiteSetting.enable_flash_video_onebox
-        "<object width='100%' height='100%'><param name='#{@url}' value='#{@url}'><embed src='#{@url}' width='100%' height='100%'></embed></object>"
+        "<object width='100%' height='100%' wmode='opaque'><param name='#{@url}' value='#{@url}'><embed src='#{@url}' width='100%' height='100%' wmode='opaque'></embed></object>"
       else
         "<a href='#{@url}'>#{@url}</a>"
       end
diff --git a/lib/oneboxer/youtube_onebox.rb b/lib/oneboxer/youtube_onebox.rb
index 6438b2f37..032352e81 100644
--- a/lib/oneboxer/youtube_onebox.rb
+++ b/lib/oneboxer/youtube_onebox.rb
@@ -8,8 +8,12 @@ module Oneboxer
     end
 
     def onebox
-      # Youtube allows HTTP and HTTPS, so replace them with the protocol-agnostic variant
-      super.each { |entry| BaseOnebox.replace_agnostic entry }
+      super.each do |entry|
+        # Youtube allows HTTP and HTTPS, so replace them with the protocol-agnostic variant
+        BaseOnebox.replace_agnostic entry
+        # Add wmode=opaque to the iframe src URL so that the flash player is rendered within the document flow instead of on top
+        BaseOnebox.append_embed_wmode entry
+      end
     end
   end
 end
diff --git a/spec/components/oneboxer/flash_video_onebox_spec.rb b/spec/components/oneboxer/flash_video_onebox_spec.rb
index 4bedd7409..9a7259f01 100644
--- a/spec/components/oneboxer/flash_video_onebox_spec.rb
+++ b/spec/components/oneboxer/flash_video_onebox_spec.rb
@@ -14,7 +14,7 @@ describe Oneboxer::FlashVideoOnebox do
 
     it "generates a flash video" do
       expect(@o.onebox).to match_html(
-        "<object width='100%' height='100%'><param name='http://player.56.com/v_OTMyNTk1MzE.swf' value='http://player.56.com/v_OTMyNTk1MzE.swf'><embed src='http://player.56.com/v_OTMyNTk1MzE.swf' width='100%' height='100%'></embed></object>" 
+        "<object width='100%' height='100%' wmode='opaque'><param name='http://player.56.com/v_OTMyNTk1MzE.swf' value='http://player.56.com/v_OTMyNTk1MzE.swf'><embed src='http://player.56.com/v_OTMyNTk1MzE.swf' width='100%' height='100%' wmode='opaque'></embed></object>"
       )
     end
   end