diff --git a/pep_sphinx_extensions/LICENCE.rst b/pep_sphinx_extensions/LICENCE.rst
index d68de666acb..4f771d4540b 100644
--- a/pep_sphinx_extensions/LICENCE.rst
+++ b/pep_sphinx_extensions/LICENCE.rst
@@ -1,2 +1,7 @@
-The files in this directory are placed in the public domain or under the
-CC0-1.0-Universal license, whichever is more permissive.
+Unless otherwise stated, the files in this directory are placed in the
+public domain or under the CC0-1.0-Universal license, whichever is more
+permissive.
+
+Some files are based on work from external projects. Check the individual
+file headers for specific licensing details. In particular:
+- lexers/asdl_lexer.py
diff --git a/pep_sphinx_extensions/lexers/asdl_lexer.py b/pep_sphinx_extensions/lexers/asdl_lexer.py
new file mode 100644
index 00000000000..62928a86698
--- /dev/null
+++ b/pep_sphinx_extensions/lexers/asdl_lexer.py
@@ -0,0 +1,53 @@
+# The code in this file is based on:
+# https://github.com/python/cpython/blob/v3.15.2/Doc/tools/extensions/lexers/asdl_lexer.py
+
+# Licensed under the Python Software Foundation License v2
+# For the full license text, see:
+# https://github.com/python/cpython/blob/v3.15.2/LICENSE
+
+from pygments.lexer import RegexLexer, bygroups, include
+from pygments.token import Comment, Keyword, Name, Operator, Punctuation, Text
+
+
+class ASDLLexer(RegexLexer):
+    name = "ASDL"
+    aliases = ["asdl"]
+    filenames = ["*.asdl"]
+    _name = r"([^\W\d]\w*)"
+    _text_ws = r"(\s*)"
+
+    tokens = {
+        "ws": [
+            (r"\n", Text),
+            (r"\s+", Text),
+            (r"--.*?$", Comment.Singleline),
+        ],
+        "root": [
+            include("ws"),
+            (
+                r"(module)" + _text_ws + _name,
+                bygroups(Keyword, Text, Name.Tag),
+            ),
+            (
+                r"(\w+)([\?\*]*\s)(\w+)",
+                bygroups(Name.Builtin.Pseudo, Operator, Name),
+            ),
+            # Keep in line with ``builtin_types`` from Parser/asdl.py.
+            # ASDL's 4 builtin types are
+            # constant, identifier, int, string
+            ("constant|identifier|int|string", Name.Builtin),
+            (r"attributes", Name.Builtin),
+            (
+                _name + _text_ws + "(=)",
+                bygroups(Name, Text, Operator),
+            ),
+            (_name, Name.Class),
+            (r"\|", Operator),
+            (r"{|}|\(|\)", Punctuation),
+            (r".", Text),
+        ],
+    }
+
+
+def register():
+    return [ASDLLexer]
diff --git a/peps/pep-0823.rst b/peps/pep-0823.rst
index 78198a86f39..64c39bb1cd4 100644
--- a/peps/pep-0823.rst
+++ b/peps/pep-0823.rst
@@ -465,7 +465,7 @@ do not support assignments themselves and thus the context will always be
 expression nodes. It is set to ``1`` if an expression is the topmost
 node in a group, ``0`` otherwise.
 
-::
+.. code-block:: ASDL
 
     expr = ...
         | Attribute(expr value, identifier attr, expr_context ctx)
diff --git a/peps/pep-0824.rst b/peps/pep-0824.rst
index c9989050a19..c6cd257133b 100644
--- a/peps/pep-0824.rst
+++ b/peps/pep-0824.rst
@@ -218,7 +218,7 @@ AST changes
 A new ``Coalesce`` operator is added to ``boolop`` for use in ``BoolOp``
 nodes.
 
-::
+.. code-block:: ASDL
 
     expr = BoolOp(boolop op, expr* values)
         | ...
@@ -284,7 +284,7 @@ A new ``BoolAssign`` AST node is added. Similar to ``AugAssign``,
 it stores a ``target`` and ``value`` expression as well as
 the boolean operator ``Coalesce``.
 
-::
+.. code-block:: ASDL
 
     stmt = ...
         | AugAssign(expr target, operator op, expr value)