diff --git a/synapse/handlers/e2e_room_keys.py b/synapse/handlers/e2e_room_keys.py
index 546050f8e..7bc174070 100644
--- a/synapse/handlers/e2e_room_keys.py
+++ b/synapse/handlers/e2e_room_keys.py
@@ -327,20 +327,35 @@ class E2eRoomKeysHandler(object):
         Returns:
             A deferred of an empty dict.
         """
-        try:
-            old_info = yield self.store.get_e2e_room_keys_version_info(user_id, version)
-        except StoreError as e:
-            if e.code == 404:
-                raise NotFoundError("Unknown backup version")
-            else:
-                raise
-        if old_info["algorithm"] != version_info["algorithm"]:
+        if "version" not in version_info:
             raise SynapseError(
                 400,
-                "Algorithm does not match",
+                "Missing version in body",
+                Codes.MISSING_PARAM
+            )
+        if version_info["version"] != version:
+            raise SynapseError(
+                400,
+                "Version in body does not match",
                 Codes.INVALID_PARAM
             )
+        with (yield self._upload_linearizer.queue(user_id)):
+            try:
+                old_info = yield self.store.get_e2e_room_keys_version_info(
+                    user_id, version
+                )
+            except StoreError as e:
+                if e.code == 404:
+                    raise NotFoundError("Unknown backup version")
+                else:
+                    raise
+            if old_info["algorithm"] != version_info["algorithm"]:
+                raise SynapseError(
+                    400,
+                    "Algorithm does not match",
+                    Codes.INVALID_PARAM
+                )
 
-        yield self.store.update_e2e_room_keys_version(user_id, version, version_info)
+            yield self.store.update_e2e_room_keys_version(user_id, version, version_info)
 
-        defer.returnValue({})
+            defer.returnValue({})
diff --git a/synapse/rest/client/v2_alpha/room_keys.py b/synapse/rest/client/v2_alpha/room_keys.py
index 1c39d2af1..220a0de30 100644
--- a/synapse/rest/client/v2_alpha/room_keys.py
+++ b/synapse/rest/client/v2_alpha/room_keys.py
@@ -394,7 +394,8 @@ class RoomKeysVersionServlet(RestServlet):
                 "signatures": {
                     "ed25519:something": "hijklmnop"
                 }
-            }
+            },
+            "version": "42"
         }
 
         HTTP/1.1 200 OK
diff --git a/tests/handlers/test_e2e_room_keys.py b/tests/handlers/test_e2e_room_keys.py
index c8994f416..1c49bbbc3 100644
--- a/tests/handlers/test_e2e_room_keys.py
+++ b/tests/handlers/test_e2e_room_keys.py
@@ -125,6 +125,78 @@ class E2eRoomKeysHandlerTestCase(unittest.TestCase):
             "auth_data": "second_version_auth_data",
         })
 
+    @defer.inlineCallbacks
+    def test_update_version(self):
+        """Check that we can update versions.
+        """
+        version = yield self.handler.create_version(self.local_user, {
+            "algorithm": "m.megolm_backup.v1",
+            "auth_data": "first_version_auth_data",
+        })
+        self.assertEqual(version, "1")
+
+        res = yield self.handler.update_version(self.local_user, version, {
+            "algorithm": "m.megolm_backup.v1",
+            "auth_data": "revised_first_version_auth_data",
+            "version": version
+        })
+        self.assertDictEqual(res, {})
+
+        # check we can retrieve it as the current version
+        res = yield self.handler.get_version_info(self.local_user)
+        self.assertDictEqual(res, {
+            "algorithm": "m.megolm_backup.v1",
+            "auth_data": "revised_first_version_auth_data",
+            "version": version
+        })
+
+    @defer.inlineCallbacks
+    def test_update_missing_version(self):
+        """Check that we get a 404 on updating nonexistent versions
+        """
+        res = None
+        try:
+            yield self.handler.update_version(self.local_user, "1", {
+                "algorithm": "m.megolm_backup.v1",
+                "auth_data": "revised_first_version_auth_data",
+                "version": "1"
+            })
+        except errors.SynapseError as e:
+            res = e.code
+        self.assertEqual(res, 404)
+
+    @defer.inlineCallbacks
+    def test_update_bad_version(self):
+        """Check that we get a 400 if the version in the body is missing or
+        doesn't match
+        """
+        version = yield self.handler.create_version(self.local_user, {
+            "algorithm": "m.megolm_backup.v1",
+            "auth_data": "first_version_auth_data",
+        })
+        self.assertEqual(version, "1")
+
+        res = None
+        try:
+            yield self.handler.update_version(self.local_user, version, {
+                "algorithm": "m.megolm_backup.v1",
+                "auth_data": "revised_first_version_auth_data"
+            })
+        except errors.SynapseError as e:
+            res = e.code
+        self.assertEqual(res, 400)
+
+        res = None
+        try:
+            yield self.handler.update_version(self.local_user, version, {
+                "algorithm": "m.megolm_backup.v1",
+                "auth_data": "revised_first_version_auth_data",
+                "version": "incorrect"
+            })
+        except errors.SynapseError as e:
+            res = e.code
+        self.assertEqual(res, 400)
+
     @defer.inlineCallbacks
     def test_delete_missing_version(self):
         """Check that we get a 404 on deleting nonexistent versions