diff --git a/crates/mdbook-html/src/html/tree.rs b/crates/mdbook-html/src/html/tree.rs
index e4da7ef6..0c7c2e4d 100644
--- a/crates/mdbook-html/src/html/tree.rs
+++ b/crates/mdbook-html/src/html/tree.rs
@@ -583,8 +583,28 @@ where
     }
 
     fn end_tag(&mut self, tag: TagEnd) {
-        // TODO: This should validate that the event stack is
-        // properly synchronized with the tag stack.
+        // TODO: This should validate that the event stack is properly
+        // synchronized with the tag stack. That, would likely require keeping
+        // a parallel "expected end tag" with the tag stack, since mapping a
+        // pulldown-cmark event tag to an HTML tag isn't always clear.
+        //
+        // Check for unclosed HTML tags when exiting a markdown event.
+        while let Some(node_id) = self.tag_stack.last() {
+            let node = self.tree.get(*node_id).unwrap().value();
+            let Node::Element(el) = node else {
+                break;
+            };
+            if !el.was_raw {
+                break;
+            }
+            warn!(
+                "unclosed HTML tag `<{}>` found in `{}` while exiting {tag:?}\n\
+                HTML tags must be closed before exiting a markdown element.",
+                el.name.local,
+                self.options.path.display(),
+            );
+            self.pop();
+        }
         self.pop();
         match tag {
             TagEnd::TableHead => {
diff --git a/tests/testsuite/rendering.rs b/tests/testsuite/rendering.rs
index ea75fbd0..421aa5d4 100644
--- a/tests/testsuite/rendering.rs
+++ b/tests/testsuite/rendering.rs
@@ -290,18 +290,17 @@ fn heading_with_unbalanced_html() {
     BookTest::init(|_| {})
         .change_file("src/chapter_1.md", "### Option<T>")
         .run("build", |cmd| {
-            cmd.expect_failure().expect_stderr(str![[r#"
+            cmd.expect_stderr(str![[r#"
  INFO Book building has started
  INFO Running the html backend
-
-thread 'main' ([..]) panicked at crates/mdbook-html/src/html/tree.rs:[..]
-internal error: expected empty tag stack.
-
-                             path: `chapter_1.md`
-element=Element { name: QualName { prefix: None, ns: Atom('http://www.w3.org/1999/xhtml' type=static), local: Atom('h3' type=inline) }, attrs: {}, self_closing: false, was_raw: false }
-note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
+ WARN unclosed HTML tag `<t>` found in `chapter_1.md` while exiting Heading(H3)
+HTML tags must be closed before exiting a markdown element.
+ INFO HTML book written to `[ROOT]/book`
 
 "#]]);
-        });
-    // .check_main_file("book/chapter_1.html", str![[""]]);
+        })
+        .check_main_file(
+            "book/chapter_1.html",
+            str![[r##"<h3 id="option"><a class="header" href="#option">Option<t></t></a></h3>"##]],
+        );
 }