diff --git a/crates/mdbook-html/src/html/tree.rs b/crates/mdbook-html/src/html/tree.rs
index 9c94a5b1f2..5a0786ea38 100644
--- a/crates/mdbook-html/src/html/tree.rs
+++ b/crates/mdbook-html/src/html/tree.rs
@@ -77,6 +77,8 @@ pub(crate) struct Element {
     pub(crate) attrs: Attributes,
     /// True if this tag ends with `/>`.
     pub(crate) self_closing: bool,
+    /// True if this was raw HTML written in the markdown.
+    pub(crate) was_raw: bool,
 }
 
 impl Element {
@@ -87,6 +89,7 @@ impl Element {
             name,
             attrs: Attributes::new(),
             self_closing: false,
+            was_raw: false,
         }
     }
 
@@ -618,6 +621,7 @@ where
                                 name,
                                 attrs,
                                 self_closing: tag.self_closing,
+                                was_raw: true,
                             };
                             fix_html_link(&mut el);
                             self.push(Node::Element(el));
@@ -842,6 +846,11 @@ where
         for heading in headings {
             let node = self.tree.get(heading).unwrap();
             let el = node.value().as_element().unwrap();
+            // Don't modify tags if they were manually written HTML. The
+            // user probably had some intent, and we don't want to mess it up.
+            if el.was_raw {
+                continue;
+            }
             let href = if let Some(id) = el.attr("id") {
                 format!("#{id}")
             } else {
diff --git a/tests/testsuite/markdown.rs b/tests/testsuite/markdown.rs
index 98fde906ce..7e46ffa228 100644
--- a/tests/testsuite/markdown.rs
+++ b/tests/testsuite/markdown.rs
@@ -157,6 +157,10 @@ fn definition_lists() {
         .check_main_file(
             "book/definition_lists.html",
             file!["markdown/definition_lists/expected_disabled/definition_lists.html"],
+        )
+        .check_main_file(
+            "book/html_definition_lists.html",
+            file!["markdown/definition_lists/expected_disabled/html_definition_lists.html"],
         );
 }
 
diff --git a/tests/testsuite/markdown/basic_markdown/expected/html.html b/tests/testsuite/markdown/basic_markdown/expected/html.html
index 7213939f8b..609fb3c717 100644
--- a/tests/testsuite/markdown/basic_markdown/expected/html.html
+++ b/tests/testsuite/markdown/basic_markdown/expected/html.html
@@ -62,4 +62,8 @@ <h2 id="style"><a class="header" href="#style">Style</a></h2>
 </style>
 <style media="(width &lt; 500px)">
 .bar { background-color: green }
-</style>
\ No newline at end of file
+</style>
+<h2 id="manual-headers"><a class="header" href="#manual-headers">Manual headers</a></h2>
+<h2 id="my header"><a href="#foo">My Header</a></h2>
+
+<h3>Another header</h3>
\ No newline at end of file
diff --git a/tests/testsuite/markdown/basic_markdown/src/html.md b/tests/testsuite/markdown/basic_markdown/src/html.md
index b2383cb452..7e33aaca0b 100644
--- a/tests/testsuite/markdown/basic_markdown/src/html.md
+++ b/tests/testsuite/markdown/basic_markdown/src/html.md
@@ -92,3 +92,9 @@ const x = 'some *text* inside';
 <style media="(width < 500px)">
 .bar { background-color: green }
 </style>
+
+## Manual headers
+
+<h2 id="my header"><a href="#foo">My Header</a></h2>
+
+<h3>Another header</h3>
diff --git a/tests/testsuite/markdown/definition_lists/expected/html_definition_lists.html b/tests/testsuite/markdown/definition_lists/expected/html_definition_lists.html
new file mode 100644
index 0000000000..50263db92c
--- /dev/null
+++ b/tests/testsuite/markdown/definition_lists/expected/html_definition_lists.html
@@ -0,0 +1,16 @@
+<h1 id="html-definition-lists"><a class="header" href="#html-definition-lists">HTML definition lists</a></h1>
+<p>Test for definition lists manually written in HTML.</p>
+<dl>
+    
+<dt>Some tag</dt>
+
+    
+<dd>Some defintion</dd>
+
+    
+<dt class="myclass" id="myid"><a class="option-anchor" href="#foo">Another definition</a></dt>
+
+    
+<dd class="def-class">A definition.</dd>
+
+</dl>
\ No newline at end of file
diff --git a/tests/testsuite/markdown/definition_lists/expected_disabled/html_definition_lists.html b/tests/testsuite/markdown/definition_lists/expected_disabled/html_definition_lists.html
new file mode 100644
index 0000000000..50263db92c
--- /dev/null
+++ b/tests/testsuite/markdown/definition_lists/expected_disabled/html_definition_lists.html
@@ -0,0 +1,16 @@
+<h1 id="html-definition-lists"><a class="header" href="#html-definition-lists">HTML definition lists</a></h1>
+<p>Test for definition lists manually written in HTML.</p>
+<dl>
+    
+<dt>Some tag</dt>
+
+    
+<dd>Some defintion</dd>
+
+    
+<dt class="myclass" id="myid"><a class="option-anchor" href="#foo">Another definition</a></dt>
+
+    
+<dd class="def-class">A definition.</dd>
+
+</dl>
\ No newline at end of file
diff --git a/tests/testsuite/markdown/definition_lists/src/SUMMARY.md b/tests/testsuite/markdown/definition_lists/src/SUMMARY.md
index 941e800019..0a93961daf 100644
--- a/tests/testsuite/markdown/definition_lists/src/SUMMARY.md
+++ b/tests/testsuite/markdown/definition_lists/src/SUMMARY.md
@@ -1,3 +1,4 @@
 # Summary
 
 - [Definition lists](./definition_lists.md)
+- [HTML definition lists](./html_definition_lists.md)
diff --git a/tests/testsuite/markdown/definition_lists/src/html_definition_lists.md b/tests/testsuite/markdown/definition_lists/src/html_definition_lists.md
new file mode 100644
index 0000000000..84de694c89
--- /dev/null
+++ b/tests/testsuite/markdown/definition_lists/src/html_definition_lists.md
@@ -0,0 +1,10 @@
+# HTML definition lists
+
+Test for definition lists manually written in HTML.
+
+<dl>
+    <dt>Some tag</dt>
+    <dd>Some defintion</dd>
+    <dt class="myclass" id="myid"><a class="option-anchor" href="#foo">Another definition</a></dt>
+    <dd class="def-class">A definition.</dd>
+</dl>