diff --git a/changelog.d/15562.misc b/changelog.d/15562.misc
new file mode 100644
index 000000000..eeeb553d8
--- /dev/null
+++ b/changelog.d/15562.misc
@@ -0,0 +1 @@
+Declare unstable support for [MSC3391](https://github.com/matrix-org/matrix-spec-proposals/pull/3391) under `/_matrix/client/versions` if the experimental implementation is enabled.
\ No newline at end of file
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 5c98916ec..2d2be6ef3 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -125,6 +125,8 @@ class VersionsRestServlet(RestServlet):
                     "org.matrix.msc3912": self.config.experimental.msc3912_enabled,
                     # Adds support for unstable "intentional mentions" behaviour.
                     "org.matrix.msc3952_intentional_mentions": self.config.experimental.msc3952_intentional_mentions,
+                    # Adds support for deleting account data.
+                    "org.matrix.msc3391": self.config.experimental.msc3391_enabled,
                 },
             },
         )