diff --git a/runtime/syntax/testdir/input/markdown_circularity.markdown b/runtime/syntax/testdir/input/markdown_circularity.markdown
new file mode 100644
index 0000000..8f442a9
--- /dev/null
+++ b/runtime/syntax/testdir/input/markdown_circularity.markdown
@@ -0,0 +1,54 @@
+No code is recognised in HTML snippets.
+
+~~~html
+<pre><code>
+/** HTML syntax circularity tests. */
+class HTMLSyntaxCircularityTests
+{
+    /// @hidden
+    ///
+    /// @param args optional command-line arguments
+    public static void main(String[] args)
+    {
+        System.out.println("""
+            ```java
+            class SyntaxCircularityTests
+            {
+                public static void main(String[] args)
+                {
+                    System.out.println(".");
+                }
+            }
+            ```
+        """);
+    }
+}
+</code></pre>
+~~~
+
+
+Markdown documentation comments are not recognised in Java snippets.
+
+```java
+/** Java syntax circularity tests. */
+class JavaSyntaxCircularityTests
+{
+    /// @hidden
+    ///
+    /// @param args optional command-line arguments
+    public static void main(String[] args)
+    {
+        System.out.println("""
+            <pre><code>
+            class SyntaxCircularityTests
+            {
+                public static void main(String[] args)
+                {
+                    System.out.println(".");
+                }
+            }
+            </code></pre>
+        """);
+    }
+}
+```
diff --git a/runtime/syntax/testdir/input/setup/markdown_circularity.vim b/runtime/syntax/testdir/input/setup/markdown_circularity.vim
new file mode 100644
index 0000000..a0b2d98
--- /dev/null
+++ b/runtime/syntax/testdir/input/setup/markdown_circularity.vim
@@ -0,0 +1,4 @@
+unlet! g:java_ignore_javadoc g:java_ignore_markdown
+let g:java_highlight_debug = 1
+let g:java_highlight_java_lang = 1
+let g:markdown_fenced_languages = ['html', 'java']