diff --git a/changelog.d/10227.feature b/changelog.d/10227.feature
new file mode 100644
index 000000000000..9c41140194b2
--- /dev/null
+++ b/changelog.d/10227.feature
@@ -0,0 +1 @@
+Implement "room knocking" as per [MSC2403](https://github.com/matrix-org/matrix-doc/pull/2403). Contributed by Sorunome and anoa.
\ No newline at end of file
diff --git a/synapse/storage/schema/main/delta/59/11add_knock_members_to_stats.sql b/synapse/storage/schema/main/delta/59/11add_knock_members_to_stats.sql
index 56c0ad000329..8eb2196f6a25 100644
--- a/synapse/storage/schema/main/delta/59/11add_knock_members_to_stats.sql
+++ b/synapse/storage/schema/main/delta/59/11add_knock_members_to_stats.sql
@@ -13,5 +13,8 @@
  * limitations under the License.
  */
 
-ALTER TABLE room_stats_current ADD COLUMN knocked_members INT NOT NULL DEFAULT '0';
-ALTER TABLE room_stats_historical ADD COLUMN knocked_members BIGINT NOT NULL DEFAULT '0';
\ No newline at end of file
+-- Existing rows will default to NULL, so anything reading from these tables
+-- needs to interpret NULL as 0. This is fine here as no existing rooms can have
+-- any knocked members.
+ALTER TABLE room_stats_current ADD COLUMN knocked_members INT;
+ALTER TABLE room_stats_historical ADD COLUMN knocked_members BIGINT;