diff --git a/changelogs/client_server/newsfragments/1600.feature b/changelogs/client_server/newsfragments/1600.feature
new file mode 100644
index 00000000..142a67b2
--- /dev/null
+++ b/changelogs/client_server/newsfragments/1600.feature
@@ -0,0 +1 @@
+Recommend that servers set a Content Security Policy for the content repository.
diff --git a/specification/modules/content_repo.rst b/specification/modules/content_repo.rst
index 0f1a9944..51cf999a 100644
--- a/specification/modules/content_repo.rst
+++ b/specification/modules/content_repo.rst
@@ -33,6 +33,10 @@ recipient's local homeserver, which must first transfer the content from the
 origin homeserver using the same API (unless the origin and destination
 homeservers are the same).
 
+When serving content, the server SHOULD provide a ``Content-Security-Policy``
+header. The recommended policy is ``default-src 'none'; script-src 'none';
+plugin-types application/pdf; style-src 'unsafe-inline'; object-src 'self';``.
+
 Client behaviour
 ----------------