diff --git a/debian/patches/0600-html-sanitizer-2.8.patch b/debian/patches/0600-html-sanitizer-2.8.patch
index 0d821a99ff..e8f6d9f46b 100644
--- a/debian/patches/0600-html-sanitizer-2.8.patch
+++ b/debian/patches/0600-html-sanitizer-2.8.patch
@@ -1,10 +1,14 @@
 https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20284
+https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/20820
 
-diff --git a/lib/banzai/filter/sanitization_filter.rb b/lib/banzai/filter/sanitization_filter.rb
-index afc2ca4e3627c5be0ea5fe73db37968cda2029bd..8275bb9e14928d56e72a75707eee3f3b082fdc4e 100644
 --- a/lib/banzai/filter/sanitization_filter.rb
 +++ b/lib/banzai/filter/sanitization_filter.rb
-@@ -4,27 +4,20 @@ module Banzai
+@@ -1,30 +1,25 @@
++# frozen_string_literal: true
++
+ module Banzai
+   module Filter
+     # Sanitize HTML
      #
      # Extends HTML::Pipeline::SanitizationFilter with a custom whitelist.
      class SanitizationFilter < HTML::Pipeline::SanitizationFilter
@@ -20,7 +24,7 @@ index afc2ca4e3627c5be0ea5fe73db37968cda2029bd..8275bb9e14928d56e72a75707eee3f3b
 -
 -        whitelist
 +        strong_memoize(:whitelist) do
-+          customize_whitelist(super.dup)
++          customize_whitelist(super.deep_dup)
 +        end
        end
  
@@ -37,3 +41,24 @@ index afc2ca4e3627c5be0ea5fe73db37968cda2029bd..8275bb9e14928d56e72a75707eee3f3b
          # Allow table alignment; we whitelist specific text-align values in a
          # transformer below
          whitelist[:attributes]['th'] = %w(style)
+--- a/spec/lib/banzai/filter/sanitization_filter_spec.rb
++++ b/spec/lib/banzai/filter/sanitization_filter_spec.rb
+@@ -54,6 +54,18 @@
+       expect(instance.whitelist[:transformers].size).to eq control_count
+     end
+ 
++    it 'customizes the whitelist only once for different instances' do
++      instance1 = described_class.new('Foo1')
++      instance2 = described_class.new('Foo2')
++      control_count = instance1.whitelist[:transformers].size
++
++      instance1.whitelist
++      instance2.whitelist
++
++      expect(instance1.whitelist[:transformers].size).to eq control_count
++      expect(instance2.whitelist[:transformers].size).to eq control_count
++    end
++
+     it 'sanitizes `class` attribute from all elements' do
+       act = %q{<pre class="code highlight white c"><code>&lt;span class="k"&gt;def&lt;/span&gt;</code></pre>}
+       exp = %q{<pre><code>&lt;span class="k"&gt;def&lt;/span&gt;</code></pre>}