diff --git a/apps/web/src/stores/widgets/ElementWidgetDriver.ts b/apps/web/src/stores/widgets/ElementWidgetDriver.ts
index 5a0a6223c2..951baefa65 100644
--- a/apps/web/src/stores/widgets/ElementWidgetDriver.ts
+++ b/apps/web/src/stores/widgets/ElementWidgetDriver.ts
@@ -139,6 +139,9 @@ export class ElementWidgetDriver extends WidgetDriver {
             this.allowedCapabilities.add(
                 WidgetEventCapability.forStateEvent(EventDirection.Receive, "org.matrix.msc3401.call").raw,
             );
+            this.allowedCapabilities.add(
+                WidgetEventCapability.forStateEvent(EventDirection.Receive, "org.matrix.msc4143.rtc.slot").raw,
+            );
             this.allowedCapabilities.add(
                 WidgetEventCapability.forStateEvent(EventDirection.Receive, EventType.RoomEncryption).raw,
             );