diff --git a/testing/web-platform/tests/interfaces/proximity.idl b/testing/web-platform/tests/interfaces/proximity.idl
index 570a29fd37b0..d4c8fae3a543 100644
--- a/testing/web-platform/tests/interfaces/proximity.idl
+++ b/testing/web-platform/tests/interfaces/proximity.idl
@@ -3,7 +3,7 @@
 // (https://github.com/tidoust/reffy-reports)
 // Source: Proximity Sensor (https://w3c.github.io/proximity/)
 
-[Constructor(optional SensorOptions sensorOptions), SecureContext, Exposed=Window]
+[Constructor(optional SensorOptions sensorOptions = {}), SecureContext, Exposed=Window]
 interface ProximitySensor : Sensor {
   readonly attribute double? distance;
   readonly attribute double? max;