diff --git a/UPGRADING.md b/UPGRADING.md
index 134ef429..b9725d3d 100644
--- a/UPGRADING.md
+++ b/UPGRADING.md
@@ -16,6 +16,7 @@ Perform EACH version specific task between your version and the new one, otherwi
 - Sessions are now stored in the database (all users have to re-login after upgrade)
 - New permissions: `lockdown_grace_timesheet`, `lockdown_override_timesheet`, `view_all_data`
 - Fixed team permissions on user queries: depending on your previous team & permission setup your users might see less data (SUPER_ADMINS see all data, but new: ADMINS only see all data if they own the `view_all_data` permission)
+- Markdown does not support headings any more, text like `# foo` is not converted to `<h1 id="foo">foo</h1>` anymore
 
 ### Developer
 
diff --git a/src/Utils/ParsedownExtension.php b/src/Utils/ParsedownExtension.php
index 0c54b78f..1589856e 100644
--- a/src/Utils/ParsedownExtension.php
+++ b/src/Utils/ParsedownExtension.php
@@ -16,6 +16,36 @@ class ParsedownExtension extends \Parsedown
 {
     private $ids = [];
 
+    /**
+     * Overwritten to prevent # to show up as headings for two reasons:
+     * - Hashes are often used to cross link issues in other systems
+     * - Headings should not occur in time record listings
+     */
+    protected $BlockTypes = [
+        '*' => ['Rule', 'List'],
+        '+' => ['List'],
+        '-' => ['SetextHeader', 'Table', 'Rule', 'List'],
+        '0' => ['List'],
+        '1' => ['List'],
+        '2' => ['List'],
+        '3' => ['List'],
+        '4' => ['List'],
+        '5' => ['List'],
+        '6' => ['List'],
+        '7' => ['List'],
+        '8' => ['List'],
+        '9' => ['List'],
+        ':' => ['Table'],
+        '<' => ['Comment', 'Markup'],
+        '=' => ['SetextHeader'],
+        '>' => ['Quote'],
+        '[' => ['Reference'],
+        '_' => ['Rule'],
+        '`' => ['FencedCode'],
+        '|' => ['Table'],
+        '~' => ['FencedCode'],
+    ];
+
     /**
      * Overwritten to add support for file:///
      */
diff --git a/tests/Twig/MarkdownExtensionTest.php b/tests/Twig/MarkdownExtensionTest.php
index 945eed22..508c4f1f 100644
--- a/tests/Twig/MarkdownExtensionTest.php
+++ b/tests/Twig/MarkdownExtensionTest.php
@@ -38,7 +38,7 @@ class MarkdownExtensionTest extends TestCase
         $config = new TimesheetConfiguration($loader, ['markdown_content' => true]);
         $sut = new MarkdownExtension(new Markdown(), $config);
         $this->assertEquals('<p><em>test</em></p>', $sut->markdownToHtml('*test*'));
-        $this->assertEquals('<h1 id="foobar">foobar</h1>', $sut->markdownToHtml('# foobar'));
+        $this->assertEquals('<p># foobar</p>', $sut->markdownToHtml('# foobar'));
     }
 
     public function testTimesheetContent()
diff --git a/tests/Utils/MarkdownTest.php b/tests/Utils/MarkdownTest.php
index 2e8a6acf..5871a5b9 100644
--- a/tests/Utils/MarkdownTest.php
+++ b/tests/Utils/MarkdownTest.php
@@ -22,21 +22,21 @@ class MarkdownTest extends TestCase
     {
         $sut = new Markdown();
         $this->assertEquals('<p><em>test</em></p>', $sut->toHtml('*test*'));
-        $this->assertEquals('<h1 id="foobar">foobar</h1>', $sut->toHtml('# foobar'));
+        $this->assertEquals('<p># foobar</p>', $sut->toHtml('# foobar'));
         $html = <<<'EOT'
 <p>foo bar</p>
 <ul>
 <li>sdfasdfasdf</li>
 <li>asdfasdfasdf</li>
 </ul>
-<h1 id="test">test</h1>
-<p>asdfasdfa</p>
+<p># test<br />
+asdfasdfa</p>
 <pre><code>ssdfsdf</code></pre>
 <p><a href="http://example.com/foo-bar.html" target="_blank">http://example.com/foo-bar.html</a><br />
 <a href="file:///home/kimai/images/beautiful-flower.png" target="_blank">file:///home/kimai/images/beautiful-flower.png</a></p>
 <p>sdfsdf <a href="#test-1">asdfasdf</a> asdfasdf</p>
-<h1 id="test-1">test</h1>
- <p>aasdfasdf<br />
+<p># test<br />
+aasdfasdf<br />
 1111<br />
 222</p>
 EOT;
@@ -70,10 +70,10 @@ EOT;
         $sut = new Markdown();
 
         $html = <<<'EOT'
-<h1 id="test">test</h1>
-<h2 id="test-1">test</h2>
-<h3 id="test-2">test</h3>
-<h1 id="test-3">test</h1>
+<p># test<br />
+## test<br />
+### test<br />
+# test</p>
 EOT;
 
         $markdown = <<<EOT