diff --git a/changelog.d/6712.feature b/changelog.d/6712.feature
new file mode 100644
index 0000000000..2cce0ecf88
--- /dev/null
+++ b/changelog.d/6712.feature
@@ -0,0 +1 @@
+Add org.matrix.e2e_cross_signing to unstable_features in /versions as per [MSC1756](https://github.com/matrix-org/matrix-doc/pull/1756).
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 2a477ad22e..3d0fefb4df 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -71,6 +71,8 @@ class VersionsRestServlet(RestServlet):
                     # Implements support for label-based filtering as described in
                     # MSC2326.
                     "org.matrix.label_based_filtering": True,
+                    # Implements support for cross signing as described in MSC1756
+                    "org.matrix.e2e_cross_signing": True,
                 },
             },
         )