diff --git a/datasette/tracer.py b/datasette/tracer.py
index 772f0405..62c3c90c 100644
--- a/datasette/tracer.py
+++ b/datasette/tracer.py
@@ -1,5 +1,6 @@
 import asyncio
 from contextlib import contextmanager
+from markupsafe import escape
 import time
 import json
 import traceback
@@ -123,7 +124,7 @@ class AsgiTracer:
                 except IndexError:
                     content_type = ""
                 if "text/html" in content_type and b"</body>" in accumulated_body:
-                    extra = json.dumps(trace_info, indent=2)
+                    extra = escape(json.dumps(trace_info, indent=2))
                     extra_html = f"<pre>{extra}</pre></body>".encode("utf8")
                     accumulated_body = accumulated_body.replace(b"</body>", extra_html)
                 elif "json" in content_type and accumulated_body.startswith(b"{"):
diff --git a/datasette/version.py b/datasette/version.py
index 4dcf73b0..aa3bef15 100644
--- a/datasette/version.py
+++ b/datasette/version.py
@@ -1,2 +1,2 @@
-__version__ = "0.56"
+__version__ = "0.56.1"
 __version_info__ = tuple(__version__.split("."))
diff --git a/docs/changelog.rst b/docs/changelog.rst
index 756badce..a4888404 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -4,6 +4,14 @@
 Changelog
 =========
 
+.. _v0_56_1:
+
+0.56.1 (2021-06-05)
+-------------------
+
+.. warning::
+    This release fixes a `reflected cross-site scripting <https://owasp.org/www-community/attacks/xss/#reflected-xss-attacks>`__ security hole with the ``?_trace=1`` feature. You should upgrade to this version, or to Datasette 0.57, as soon as possible. (:issue:`1360`)
+
 .. _v0_56:
 
 0.56 (2021-03-28)
diff --git a/tests/test_html.py b/tests/test_html.py
index 9e86ebc2..d15e7e57 100644
--- a/tests/test_html.py
+++ b/tests/test_html.py
@@ -1612,3 +1612,9 @@ def test_navigation_menu_links(
             assert (
                 details.find("a", {"href": link}) is None
             ), f"{link} found but should not have been in nav menu"
+
+
+def test_trace_correctly_escaped(app_client):
+    response = app_client.get("/fixtures?sql=select+'<h1>Hello'&_trace=1")
+    assert "select '<h1>Hello" not in response.text
+    assert "select &#39;&lt;h1&gt;Hello" in response.text