diff --git a/synapse/handlers/e2e_keys.py b/synapse/handlers/e2e_keys.py
index 73572f4614..d25af42f5f 100644
--- a/synapse/handlers/e2e_keys.py
+++ b/synapse/handlers/e2e_keys.py
@@ -55,8 +55,9 @@ class E2eKeysHandler(object):
 
         federation_registry = hs.get_federation_registry()
 
+        # FIXME: switch to m.signing_key_update when MSC1756 is merged into the spec
         federation_registry.register_edu_handler(
-            "m.signing_key_update", self._edu_updater.incoming_signing_key_update
+            "org.matrix.signing_key_update", self._edu_updater.incoming_signing_key_update
         )
         # doesn't really work as part of the generic query API, because the
         # query request requires an object POST, but we abuse the
diff --git a/synapse/storage/devices.py b/synapse/storage/devices.py
index 1aaef1fbb0..6ac165068e 100644
--- a/synapse/storage/devices.py
+++ b/synapse/storage/devices.py
@@ -231,7 +231,8 @@ class DeviceWorkerStore(SQLBaseStore):
         # add the updated cross-signing keys to the results list
         for user_id, result in iteritems(cross_signing_keys_by_user):
             result["user_id"] = user_id
-            cross_signing_results.append(("m.signing_key_update", result))
+            # FIXME: switch to m.signing_key_update when MSC1756 is merged into the spec
+            cross_signing_results.append(("org.matrix.signing_key_update", result))
 
         # That should only happen if a client is spamming the server with new
         # devices, in which case E2E isn't going to work well anyway. We'll just