diff --git a/lib/yard/templates/helpers/html_helper.rb b/lib/yard/templates/helpers/html_helper.rb
index 4d3d56862..0801ca35a 100644
--- a/lib/yard/templates/helpers/html_helper.rb
+++ b/lib/yard/templates/helpers/html_helper.rb
@@ -54,7 +54,7 @@ def urlencode(text)
       # @param [Symbol] markup examples are +:markdown+, +:textile+, +:rdoc+.
       #   To add a custom markup type, see {MarkupHelper}
       # @return [String] the HTML
-      def htmlify(text, markup = options.markup)
+      def htmlify(text, markup = options.markup, internal = false)
         markup_meth = "html_markup_#{markup}"
         return text unless respond_to?(markup_meth)
         return "" unless text
@@ -66,7 +66,7 @@ def htmlify(text, markup = options.markup)
         end
         html = resolve_links(html)
         unless [:text, :none, :pre, :ruby].include?(markup)
-          html = parse_codeblocks(html)
+          html = parse_codeblocks(html, internal)
         end
         html
       end
@@ -202,6 +202,11 @@ def html_syntax_highlight(source, type = nil)
 
         new_type, source = parse_lang_for_codeblock(source)
         type ||= new_type || :ruby
+
+        if type.to_s == "ruby" && source =~ /<span\s+class=/
+          return source
+        end
+
         meth = "html_syntax_highlight_#{type}"
         respond_to?(meth) ? send(meth, source) : h(source)
       end
@@ -294,7 +299,7 @@ def link_include_object(obj)
 
       # Inserts an include link while respecting inlining
       def insert_include(text, markup = options.markup)
-        htmlify(text, markup).gsub(%r{\A\s*<p>|</p>\s*\Z}, '')
+        htmlify(text, markup, true).gsub(%r{\A\s*<p>|</p>\s*\Z}, '')
       end
 
       # (see BaseHelper#link_object)
@@ -637,20 +642,25 @@ def parse_lang_for_codeblock(source)
       # @param [String] html the html to search for code in
       # @return [String] highlighted html
       # @see #html_syntax_highlight
-      def parse_codeblocks(html)
+      def parse_codeblocks(html, internal = false)
         html.gsub(%r{<pre((?:\s+\w+="(?:.+?)")*)\s*>(?:\s*<code((?:\s+\w+="(?:.+?)")*)\s*>)?(.+?)(?:</code>\s*)?</pre>}m) do
-          string = $3
+          pre_match, code_match, string = $1, $2, $3
 
           # handle !!!LANG prefix to send to html_syntax_highlight_LANG
           language, = parse_lang_for_codeblock(string)
-          language ||= detect_lang_in_codeblock_attributes($1, $2)
+          language ||= detect_lang_in_codeblock_attributes(pre_match, code_match)
           language ||= object.source_type
 
-          if options.highlight
+          pre_attrs = [%(class="code #{language}")]
+
+          if options.highlight && /\bdata-highlighted="true"/ !~ pre_match
             string = html_syntax_highlight(CGI.unescapeHTML(string), language)
+            pre_attrs << 'data-highlighted="true"' if internal
           end
-          classes = ['code', language].compact.join(' ')
-          %(<pre class="#{classes}"><code class="#{language}">#{string}</code></pre>)
+
+          pre_attrs = pre_attrs.compact.join(' ')
+
+          %(<pre #{pre_attrs}><code class="#{language}">#{string}</code></pre>)
         end
       end
 
diff --git a/lib/yard/templates/helpers/html_syntax_highlight_helper.rb b/lib/yard/templates/helpers/html_syntax_highlight_helper.rb
index 07ab9be79..fc5c60cee 100644
--- a/lib/yard/templates/helpers/html_syntax_highlight_helper.rb
+++ b/lib/yard/templates/helpers/html_syntax_highlight_helper.rb
@@ -39,7 +39,7 @@ def html_syntax_highlight_ruby_ripper(source)
           end
           output
         rescue Parser::ParserSyntaxError
-          source =~ /^<span\s+class=/ ? source : h(source)
+          h(source)
         end
 
         def html_syntax_highlight_ruby_legacy(source)
diff --git a/spec/templates/helpers/html_helper_spec.rb b/spec/templates/helpers/html_helper_spec.rb
index 5f3f268a5..133fbb1e1 100644
--- a/spec/templates/helpers/html_helper_spec.rb
+++ b/spec/templates/helpers/html_helper_spec.rb
@@ -144,6 +144,30 @@ def options
       expect(htmlify("test {include:file:foo.rdoc}", :rdoc).gsub(/[\r?\n]+/, '')).to eq '<p>test HI</p>'
     end
 
+    it "preserves syntax highlighting in {include:} snippets" do
+      load_markup_provider(:rdoc)
+      expect(File).to receive(:file?).with('foo.rdoc').and_return(true)
+      expect(File).to receive(:read).with('foo.rdoc').and_return(
+                        " !!!ruby\n x = 1\n"
+                      )
+      expect(htmlify("{include:file:foo.rdoc}", :rdoc).gsub(/[\r?\n]+/, '')).
+        not_to include("&lt;")
+    end
+
+    it "escapes {include:} html snippets only once" do
+      expect(self).to receive(:html_syntax_highlight_html) do |source|
+        %(<strong>#{CGI.escapeHTML(source)}</strong>)
+      end.at_least(:once)
+
+      load_markup_provider(:rdoc)
+      expect(File).to receive(:file?).with('foo.md').and_return(true)
+      expect(File).to receive(:read).with('foo.md').and_return(
+                        "    !!!html\n    <h1>\n"
+                      )
+      expect(htmlify("{include:file:foo.md}", :markdown).gsub(/[\r?\n]+/, '')).
+        to include(%(<strong>&lt;h1&gt;</strong>))
+    end
+
     it "does not autolink URLs inside of {} (markdown specific)" do
       log.enter_level(Logger::FATAL) do
         pending 'This test depends on markdown' unless markup_class(:markdown)
@@ -648,6 +672,12 @@ def subject.respond_to?(method, include_all = false)
       )
     end
 
+    it "wraps but doesn't alter ruby snippets that already contain highlighting tags" do
+      expect(subject.htmlify('<pre lang="ruby"><span class="kw">for</span></pre>', :html)).to eq(
+        '<pre class="code ruby"><code class="ruby"><span class="kw">for</span></code></pre>'
+      )
+    end
+
     it "highlights source when matching a pre lang= tag" do
       expect(subject.htmlify('<pre lang="foo"><code>x = 1</code></pre>', :html)).to eq(
         '<pre class="code foo"><code class="foo">x = 1</code></pre>'