diff --git a/src/main/scala-3/org/scalajs/dom/AppendMode.scala b/src/main/scala-3/org/scalajs/dom/AppendMode.scala
index b7928f08f..82a39e171 100644
--- a/src/main/scala-3/org/scalajs/dom/AppendMode.scala
+++ b/src/main/scala-3/org/scalajs/dom/AppendMode.scala
@@ -1,6 +1,6 @@
 package org.scalajs.dom
 
-opaque type AppendMode = String
+opaque type AppendMode <: String = String
 
 object AppendMode {
   val segments: AppendMode = "segments"
diff --git a/src/main/scala-3/org/scalajs/dom/ClientType.scala b/src/main/scala-3/org/scalajs/dom/ClientType.scala
index adec227ef..17347e98d 100644
--- a/src/main/scala-3/org/scalajs/dom/ClientType.scala
+++ b/src/main/scala-3/org/scalajs/dom/ClientType.scala
@@ -2,7 +2,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type ClientType = String
+opaque type ClientType <: String = String
 
 object ClientType {
   val window: ClientType = "window"
diff --git a/src/main/scala-3/org/scalajs/dom/EndOfStreamError.scala b/src/main/scala-3/org/scalajs/dom/EndOfStreamError.scala
index 1f4772976..10fb0b3a7 100644
--- a/src/main/scala-3/org/scalajs/dom/EndOfStreamError.scala
+++ b/src/main/scala-3/org/scalajs/dom/EndOfStreamError.scala
@@ -1,6 +1,6 @@
 package org.scalajs.dom
 
-opaque type EndOfStreamError = String
+opaque type EndOfStreamError <: String = String
 
 object EndOfStreamError {
   val decode: EndOfStreamError = "decode"
diff --git a/src/main/scala-3/org/scalajs/dom/FrameType.scala b/src/main/scala-3/org/scalajs/dom/FrameType.scala
index 7ce70a97d..153488aac 100644
--- a/src/main/scala-3/org/scalajs/dom/FrameType.scala
+++ b/src/main/scala-3/org/scalajs/dom/FrameType.scala
@@ -2,7 +2,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type FrameType = String
+opaque type FrameType <: String = String
 
 /** part of ServiceWorker
   * [[https://slightlyoff.github.io/ServiceWorker/spec/service_worker_1/#client-frametype ¶4.2.2 frameType]] of
diff --git a/src/main/scala-3/org/scalajs/dom/IDBTransactionDurability.scala b/src/main/scala-3/org/scalajs/dom/IDBTransactionDurability.scala
index 861e2eb96..ab364d5e5 100644
--- a/src/main/scala-3/org/scalajs/dom/IDBTransactionDurability.scala
+++ b/src/main/scala-3/org/scalajs/dom/IDBTransactionDurability.scala
@@ -8,7 +8,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type IDBTransactionDurability = String
+opaque type IDBTransactionDurability <: String = String
 
 object IDBTransactionDurability {
   val default: IDBTransactionDurability = "default"
diff --git a/src/main/scala-3/org/scalajs/dom/IDBTransactionMode.scala b/src/main/scala-3/org/scalajs/dom/IDBTransactionMode.scala
index 0dfad9e60..0abafff61 100644
--- a/src/main/scala-3/org/scalajs/dom/IDBTransactionMode.scala
+++ b/src/main/scala-3/org/scalajs/dom/IDBTransactionMode.scala
@@ -11,7 +11,7 @@ import scala.scalajs.js
 /** IndexedDB transaction mode Provides constants for IDB Transaction modes These constants have been removed from
   * browser support and replaced by String values
   */
-opaque type IDBTransactionMode = String
+opaque type IDBTransactionMode <: String = String
 
 object IDBTransactionMode {
 
diff --git a/src/main/scala-3/org/scalajs/dom/KeyFormat.scala b/src/main/scala-3/org/scalajs/dom/KeyFormat.scala
index aec989ed1..6e5efab2b 100644
--- a/src/main/scala-3/org/scalajs/dom/KeyFormat.scala
+++ b/src/main/scala-3/org/scalajs/dom/KeyFormat.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** see [[http://www.w3.org/TR/WebCryptoAPI/#dfn-KeyFormat ¶14.2 Data Types]] in W3C spec */
-opaque type KeyFormat = String
+opaque type KeyFormat <: String = String
 
 object KeyFormat {
 
diff --git a/src/main/scala-3/org/scalajs/dom/KeyType.scala b/src/main/scala-3/org/scalajs/dom/KeyType.scala
index 073aadd9c..d3d1d2ff3 100644
--- a/src/main/scala-3/org/scalajs/dom/KeyType.scala
+++ b/src/main/scala-3/org/scalajs/dom/KeyType.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** see [[http://www.w3.org/TR/WebCryptoAPI/#cryptokey-interface ¶13 CryptoKey interface]] in W3C doc */
-opaque type KeyType = String
+opaque type KeyType <: String = String
 
 object KeyType {
   val public: KeyType = "public"
diff --git a/src/main/scala-3/org/scalajs/dom/KeyUsage.scala b/src/main/scala-3/org/scalajs/dom/KeyUsage.scala
index 7b300ab6a..0fef106b1 100644
--- a/src/main/scala-3/org/scalajs/dom/KeyUsage.scala
+++ b/src/main/scala-3/org/scalajs/dom/KeyUsage.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** See [[http://www.w3.org/TR/WebCryptoAPI/#cryptokey-interface ¶ 13. CryptoKey Interface]] of w3c spec */
-opaque type KeyUsage = String
+opaque type KeyUsage <: String = String
 
 object KeyUsage {
   val encrypt: KeyUsage = "encrypt"
diff --git a/src/main/scala-3/org/scalajs/dom/MIMEType.scala b/src/main/scala-3/org/scalajs/dom/MIMEType.scala
index 40cb8b7da..8346a8640 100644
--- a/src/main/scala-3/org/scalajs/dom/MIMEType.scala
+++ b/src/main/scala-3/org/scalajs/dom/MIMEType.scala
@@ -2,7 +2,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type MIMEType = String
+opaque type MIMEType <: String = String
 
 object MIMEType {
   val `text/html`: MIMEType = "text/html"
diff --git a/src/main/scala-3/org/scalajs/dom/MediaDeviceKind.scala b/src/main/scala-3/org/scalajs/dom/MediaDeviceKind.scala
index 0e7d4267f..aacaed14b 100644
--- a/src/main/scala-3/org/scalajs/dom/MediaDeviceKind.scala
+++ b/src/main/scala-3/org/scalajs/dom/MediaDeviceKind.scala
@@ -4,7 +4,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** see [[https://www.w3.org/TR/2016/CR-mediacapture-streams-20160519/#idl-def-MediaDeviceKind]] in W3C spec */
-opaque type MediaDeviceKind = String
+opaque type MediaDeviceKind <: String = String
 
 object MediaDeviceKind {
 
diff --git a/src/main/scala-3/org/scalajs/dom/MediaStreamTrackState.scala b/src/main/scala-3/org/scalajs/dom/MediaStreamTrackState.scala
index cb51d86de..45d63e857 100644
--- a/src/main/scala-3/org/scalajs/dom/MediaStreamTrackState.scala
+++ b/src/main/scala-3/org/scalajs/dom/MediaStreamTrackState.scala
@@ -4,7 +4,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** see [[https://www.w3.org/TR/2013/WD-mediacapture-streams-20130903/#widl-MediaStream-onended]] in W3C spec */
-opaque type MediaStreamTrackState = String
+opaque type MediaStreamTrackState <: String = String
 
 object MediaStreamTrackState {
 
diff --git a/src/main/scala-3/org/scalajs/dom/PermissionName.scala b/src/main/scala-3/org/scalajs/dom/PermissionName.scala
index c7013a3da..45b358b9a 100644
--- a/src/main/scala-3/org/scalajs/dom/PermissionName.scala
+++ b/src/main/scala-3/org/scalajs/dom/PermissionName.scala
@@ -2,7 +2,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type PermissionName = String
+opaque type PermissionName <: String = String
 
 object PermissionName {
   val geolocation: PermissionName = "geolocation"
diff --git a/src/main/scala-3/org/scalajs/dom/PermissionState.scala b/src/main/scala-3/org/scalajs/dom/PermissionState.scala
index 65544a216..8a9c761f3 100644
--- a/src/main/scala-3/org/scalajs/dom/PermissionState.scala
+++ b/src/main/scala-3/org/scalajs/dom/PermissionState.scala
@@ -2,7 +2,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type PermissionState = String
+opaque type PermissionState <: String = String
 
 object PermissionState {
   val granted: PermissionState = "granted"
diff --git a/src/main/scala-3/org/scalajs/dom/PushEncryptionKeyName.scala b/src/main/scala-3/org/scalajs/dom/PushEncryptionKeyName.scala
index f6a214625..1f90b4648 100644
--- a/src/main/scala-3/org/scalajs/dom/PushEncryptionKeyName.scala
+++ b/src/main/scala-3/org/scalajs/dom/PushEncryptionKeyName.scala
@@ -5,7 +5,7 @@ import scala.scalajs.js
 /** This represents a JavaScript enumeration representing the various keys you an request from a [[PushSubscription]] as
   * described here: [[http://www.w3.org/TR/push-api/#idl-def-PushEncryptionKeyName]]
   */
-opaque type PushEncryptionKeyName = String
+opaque type PushEncryptionKeyName <: String = String
 
 /** Static definitions for [[PushEncryptionKeyName]] */
 object PushEncryptionKeyName {
diff --git a/src/main/scala-3/org/scalajs/dom/PushPermissionState.scala b/src/main/scala-3/org/scalajs/dom/PushPermissionState.scala
index 3520703c1..ae0b6902c 100644
--- a/src/main/scala-3/org/scalajs/dom/PushPermissionState.scala
+++ b/src/main/scala-3/org/scalajs/dom/PushPermissionState.scala
@@ -5,7 +5,7 @@ import scala.scalajs.js
 /** This represents a JavaScript enumeration describing the state of permissions for pushing described here:
   * [[http://www.w3.org/TR/push-api/#idl-def-PushPermissionState]]
   */
-opaque type PushPermissionState = String
+opaque type PushPermissionState <: String = String
 
 /** Static definitions for [[PushPermissionState]] */
 object PushPermissionState {
diff --git a/src/main/scala-3/org/scalajs/dom/RTCBundlePolicy.scala b/src/main/scala-3/org/scalajs/dom/RTCBundlePolicy.scala
index 4ff7f73b0..59ff049f0 100644
--- a/src/main/scala-3/org/scalajs/dom/RTCBundlePolicy.scala
+++ b/src/main/scala-3/org/scalajs/dom/RTCBundlePolicy.scala
@@ -4,7 +4,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** see [[https://www.w3.org/TR/2015/WD-webrtc-20150210/#idl-def-RTCBundlePolicy]] in W3C spec */
-opaque type RTCBundlePolicy = String
+opaque type RTCBundlePolicy <: String = String
 
 object RTCBundlePolicy {
 
diff --git a/src/main/scala-3/org/scalajs/dom/RTCDataChannelState.scala b/src/main/scala-3/org/scalajs/dom/RTCDataChannelState.scala
index 780c0a6f5..2076a5a88 100644
--- a/src/main/scala-3/org/scalajs/dom/RTCDataChannelState.scala
+++ b/src/main/scala-3/org/scalajs/dom/RTCDataChannelState.scala
@@ -4,7 +4,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** see [[https://www.w3.org/TR/2015/WD-webrtc-20150210/#idl-def-RTCDataChannelState]] in W3C spec */
-opaque type RTCDataChannelState = String
+opaque type RTCDataChannelState <: String = String
 
 object RTCDataChannelState {
 
diff --git a/src/main/scala-3/org/scalajs/dom/RTCIceConnectionState.scala b/src/main/scala-3/org/scalajs/dom/RTCIceConnectionState.scala
index 2cab2abaa..1a7c5b634 100644
--- a/src/main/scala-3/org/scalajs/dom/RTCIceConnectionState.scala
+++ b/src/main/scala-3/org/scalajs/dom/RTCIceConnectionState.scala
@@ -4,7 +4,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** see [[https://www.w3.org/TR/2015/WD-webrtc-20150210/#rtciceconnectionstate-enum]] in W3C spec */
-opaque type RTCIceConnectionState = String
+opaque type RTCIceConnectionState <: String = String
 
 object RTCIceConnectionState {
 
diff --git a/src/main/scala-3/org/scalajs/dom/RTCIceGatheringState.scala b/src/main/scala-3/org/scalajs/dom/RTCIceGatheringState.scala
index f94c6f65c..1d88928bd 100644
--- a/src/main/scala-3/org/scalajs/dom/RTCIceGatheringState.scala
+++ b/src/main/scala-3/org/scalajs/dom/RTCIceGatheringState.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type RTCIceGatheringState = String
+opaque type RTCIceGatheringState <: String = String
 
 object RTCIceGatheringState {
 
diff --git a/src/main/scala-3/org/scalajs/dom/RTCIceTransportPolicy.scala b/src/main/scala-3/org/scalajs/dom/RTCIceTransportPolicy.scala
index 9dac209d9..b2bfd6813 100644
--- a/src/main/scala-3/org/scalajs/dom/RTCIceTransportPolicy.scala
+++ b/src/main/scala-3/org/scalajs/dom/RTCIceTransportPolicy.scala
@@ -4,7 +4,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** see [[https://www.w3.org/TR/2015/WD-webrtc-20150210/#idl-def-RTCIceTransportPolicy]] in W3C spec */
-opaque type RTCIceTransportPolicy = String
+opaque type RTCIceTransportPolicy <: String = String
 
 object RTCIceTransportPolicy {
 
diff --git a/src/main/scala-3/org/scalajs/dom/RTCSdpType.scala b/src/main/scala-3/org/scalajs/dom/RTCSdpType.scala
index 03bfc4e3b..8f5fb2f3d 100644
--- a/src/main/scala-3/org/scalajs/dom/RTCSdpType.scala
+++ b/src/main/scala-3/org/scalajs/dom/RTCSdpType.scala
@@ -4,7 +4,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** see [[https://www.w3.org/TR/2015/WD-webrtc-20150210/#idl-def-RTCSdpType]] in W3C spec */
-opaque type RTCSdpType = String
+opaque type RTCSdpType <: String = String
 
 object RTCSdpType {
 
diff --git a/src/main/scala-3/org/scalajs/dom/RTCSignalingState.scala b/src/main/scala-3/org/scalajs/dom/RTCSignalingState.scala
index 81ab9175a..696121f95 100644
--- a/src/main/scala-3/org/scalajs/dom/RTCSignalingState.scala
+++ b/src/main/scala-3/org/scalajs/dom/RTCSignalingState.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type RTCSignalingState = String
+opaque type RTCSignalingState <: String = String
 
 object RTCSignalingState {
 
diff --git a/src/main/scala-3/org/scalajs/dom/RTCStatsType.scala b/src/main/scala-3/org/scalajs/dom/RTCStatsType.scala
index 41b6d7038..31086734c 100644
--- a/src/main/scala-3/org/scalajs/dom/RTCStatsType.scala
+++ b/src/main/scala-3/org/scalajs/dom/RTCStatsType.scala
@@ -4,7 +4,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** see [[https://www.w3.org/TR/2015/WD-webrtc-20150210/#idl-def-RTCStatsType]] in W3C spec */
-opaque type RTCStatsType = String
+opaque type RTCStatsType <: String = String
 
 object RTCStatsType {
 
diff --git a/src/main/scala-3/org/scalajs/dom/ReadyState.scala b/src/main/scala-3/org/scalajs/dom/ReadyState.scala
index 9465ad0e0..b69c7de45 100644
--- a/src/main/scala-3/org/scalajs/dom/ReadyState.scala
+++ b/src/main/scala-3/org/scalajs/dom/ReadyState.scala
@@ -1,6 +1,6 @@
 package org.scalajs.dom
 
-opaque type ReadyState = String
+opaque type ReadyState <: String = String
 
 object ReadyState {
   val closed: ReadyState = "closed"
diff --git a/src/main/scala-3/org/scalajs/dom/ReferrerPolicy.scala b/src/main/scala-3/org/scalajs/dom/ReferrerPolicy.scala
index 118b34453..91b576106 100644
--- a/src/main/scala-3/org/scalajs/dom/ReferrerPolicy.scala
+++ b/src/main/scala-3/org/scalajs/dom/ReferrerPolicy.scala
@@ -2,7 +2,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type ReferrerPolicy = String
+opaque type ReferrerPolicy <: String = String
 
 object ReferrerPolicy {
   val empty: ReferrerPolicy = ""
diff --git a/src/main/scala-3/org/scalajs/dom/RequestCache.scala b/src/main/scala-3/org/scalajs/dom/RequestCache.scala
index 6df97619a..58c7b0843 100644
--- a/src/main/scala-3/org/scalajs/dom/RequestCache.scala
+++ b/src/main/scala-3/org/scalajs/dom/RequestCache.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** Fetch APIs [[https://fetch.spec.whatwg.org/#requestcache RequestCache enum]] */
-opaque type RequestCache = String
+opaque type RequestCache <: String = String
 
 object RequestCache {
   val default: RequestCache = "default"
diff --git a/src/main/scala-3/org/scalajs/dom/RequestCredentials.scala b/src/main/scala-3/org/scalajs/dom/RequestCredentials.scala
index f8b873498..b868d62c0 100644
--- a/src/main/scala-3/org/scalajs/dom/RequestCredentials.scala
+++ b/src/main/scala-3/org/scalajs/dom/RequestCredentials.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** Fetch APIs [[https://fetch.spec.whatwg.org/#requestcredentials RequestCredentials enum]] */
-opaque type RequestCredentials = String
+opaque type RequestCredentials <: String = String
 
 object RequestCredentials {
   val omit: RequestCredentials = "omit"
diff --git a/src/main/scala-3/org/scalajs/dom/RequestDestination.scala b/src/main/scala-3/org/scalajs/dom/RequestDestination.scala
index 41143b9bf..d24b692e2 100644
--- a/src/main/scala-3/org/scalajs/dom/RequestDestination.scala
+++ b/src/main/scala-3/org/scalajs/dom/RequestDestination.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** Fetch APIs [[https://fetch.spec.whatwg.org/#requestdestination RequestDestination enum]] */
-opaque type RequestDestination = String
+opaque type RequestDestination <: String = String
 
 object RequestDestination {
   val empty: RequestDestination = ""
diff --git a/src/main/scala-3/org/scalajs/dom/RequestMode.scala b/src/main/scala-3/org/scalajs/dom/RequestMode.scala
index 832015f7e..ffe970dd6 100644
--- a/src/main/scala-3/org/scalajs/dom/RequestMode.scala
+++ b/src/main/scala-3/org/scalajs/dom/RequestMode.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** Fetch API's [[https://fetch.spec.whatwg.org/#requestmode RequestMode enum]] */
-opaque type RequestMode = String
+opaque type RequestMode <: String = String
 
 object RequestMode {
   val navigate: RequestMode = "navigate"
diff --git a/src/main/scala-3/org/scalajs/dom/RequestRedirect.scala b/src/main/scala-3/org/scalajs/dom/RequestRedirect.scala
index 6398a62ce..ff3f675f8 100644
--- a/src/main/scala-3/org/scalajs/dom/RequestRedirect.scala
+++ b/src/main/scala-3/org/scalajs/dom/RequestRedirect.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** Fetch API's [[https://fetch.spec.whatwg.org/#requestredirect RequestRedirect enum]] */
-opaque type RequestRedirect = String
+opaque type RequestRedirect <: String = String
 
 object RequestRedirect {
   val follow: RequestRedirect = "follow"
diff --git a/src/main/scala-3/org/scalajs/dom/RequestType.scala b/src/main/scala-3/org/scalajs/dom/RequestType.scala
index c79e7f449..87d11c144 100644
--- a/src/main/scala-3/org/scalajs/dom/RequestType.scala
+++ b/src/main/scala-3/org/scalajs/dom/RequestType.scala
@@ -3,7 +3,7 @@ package org.scalajs.dom
 import scala.scalajs.js
 
 /** Fetch APIs [[https://fetch.spec.whatwg.org/#requesttype RequestType enum]] */
-opaque type RequestType = String
+opaque type RequestType <: String = String
 
 object RequestType {
   val empty: RequestType = ""
diff --git a/src/main/scala-3/org/scalajs/dom/ResponseType.scala b/src/main/scala-3/org/scalajs/dom/ResponseType.scala
index b1d50a1ed..d38caf210 100644
--- a/src/main/scala-3/org/scalajs/dom/ResponseType.scala
+++ b/src/main/scala-3/org/scalajs/dom/ResponseType.scala
@@ -2,7 +2,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type ResponseType = String
+opaque type ResponseType <: String = String
 
 /** see [[https://fetch.spec.whatwg.org/#responsetype]] of whatwg Fetch spec */
 object ResponseType {
diff --git a/src/main/scala-3/org/scalajs/dom/ServiceWorkerState.scala b/src/main/scala-3/org/scalajs/dom/ServiceWorkerState.scala
index f848788e0..8580aecb3 100644
--- a/src/main/scala-3/org/scalajs/dom/ServiceWorkerState.scala
+++ b/src/main/scala-3/org/scalajs/dom/ServiceWorkerState.scala
@@ -5,7 +5,7 @@ import scala.scalajs.js
 /** See [[https://slightlyoff.github.io/ServiceWorker/spec/service_worker_1/#service-worker-obj ¶3.1 ServiceWorker]] of
   * ServiceWorker whatwg spec.
   */
-opaque type ServiceWorkerState = String
+opaque type ServiceWorkerState <: String = String
 
 object ServiceWorkerState {
 
diff --git a/src/main/scala-3/org/scalajs/dom/TextTrackMode.scala b/src/main/scala-3/org/scalajs/dom/TextTrackMode.scala
index e96102f73..0f4b836fd 100644
--- a/src/main/scala-3/org/scalajs/dom/TextTrackMode.scala
+++ b/src/main/scala-3/org/scalajs/dom/TextTrackMode.scala
@@ -1,6 +1,6 @@
 package org.scalajs.dom
 
-opaque type TextTrackMode = String
+opaque type TextTrackMode <: String = String
 
 object TextTrackMode {
   val disabled: TextTrackMode = "disabled"
diff --git a/src/main/scala-3/org/scalajs/dom/VisibilityState.scala b/src/main/scala-3/org/scalajs/dom/VisibilityState.scala
index da02444a2..18f218193 100644
--- a/src/main/scala-3/org/scalajs/dom/VisibilityState.scala
+++ b/src/main/scala-3/org/scalajs/dom/VisibilityState.scala
@@ -8,7 +8,7 @@ package org.scalajs.dom
 
 import scala.scalajs.js
 
-opaque type VisibilityState = String
+opaque type VisibilityState <: String = String
 
 object VisibilityState {
 
diff --git a/src/main/scala-3/org/scalajs/dom/WriteableState.scala b/src/main/scala-3/org/scalajs/dom/WriteableState.scala
index 46a72e086..fd3db4b3b 100644
--- a/src/main/scala-3/org/scalajs/dom/WriteableState.scala
+++ b/src/main/scala-3/org/scalajs/dom/WriteableState.scala
@@ -5,7 +5,7 @@ import scala.scalajs.js
 // the stream API is defined in https://streams.spec.whatwg.org/
 
 /** [[https://streams.spec.whatwg.org/#ws-state ¶4.2.4.3. get state]] of whatwg streams spec */
-opaque type WriteableState = String
+opaque type WriteableState <: String = String
 
 object WriteableState {
 
diff --git a/src/main/scala/org/scalajs/dom/RTCConfiguration.scala b/src/main/scala/org/scalajs/dom/RTCConfiguration.scala
index ae0652ba3..dbb1f7726 100644
--- a/src/main/scala/org/scalajs/dom/RTCConfiguration.scala
+++ b/src/main/scala/org/scalajs/dom/RTCConfiguration.scala
@@ -31,9 +31,9 @@ object RTCConfiguration {
       peerIdentity: js.UndefOr[String] = js.undefined): RTCConfiguration = {
     val result = js.Dynamic.literal()
     iceServers.foreach(result.iceServers = _)
-    iceTransportPolicy.foreach(x => result.iceTransportPolicy = x.asInstanceOf[js.Any])
-    bundlePolicy.foreach(x => result.bundlePolicy = x.asInstanceOf[js.Any])
-    peerIdentity.foreach(x => result.peerIdentity = x.asInstanceOf[js.Any])
+    iceTransportPolicy.foreach(result.iceTransportPolicy = _)
+    bundlePolicy.foreach(result.bundlePolicy = _)
+    peerIdentity.foreach(result.peerIdentity = _)
     result.asInstanceOf[RTCConfiguration]
   }
 }
diff --git a/src/main/scala/org/scalajs/dom/RTCSessionDescriptionInit.scala b/src/main/scala/org/scalajs/dom/RTCSessionDescriptionInit.scala
index 594305546..4b08152dc 100644
--- a/src/main/scala/org/scalajs/dom/RTCSessionDescriptionInit.scala
+++ b/src/main/scala/org/scalajs/dom/RTCSessionDescriptionInit.scala
@@ -16,7 +16,7 @@ object RTCSessionDescriptionInit {
   def apply(`type`: js.UndefOr[RTCSdpType] = js.undefined,
       sdp: js.UndefOr[String] = js.undefined): RTCSessionDescriptionInit = {
     val result = js.Dynamic.literal()
-    `type`.foreach(x => result.`type` = x.asInstanceOf[js.Any])
+    `type`.foreach(result.`type` = _)
     sdp.foreach(result.sdp = _)
     result.asInstanceOf[RTCSessionDescriptionInit]
   }