diff --git a/baselines/dom.generated.d.ts b/baselines/dom.generated.d.ts
index 70e23ef78..d7c6b6e0e 100644
--- a/baselines/dom.generated.d.ts
+++ b/baselines/dom.generated.d.ts
@@ -215,6 +215,14 @@ interface AuthenticationExtensionsClientOutputs {
     prf?: AuthenticationExtensionsPRFOutputs;
 }
 
+interface AuthenticationExtensionsClientOutputsJSON {
+    appid?: boolean;
+    appidExclude?: boolean;
+    credProps?: CredentialPropertiesOutput;
+    largeBlob?: AuthenticationExtensionsLargeBlobOutputsJSON;
+    prf?: AuthenticationExtensionsPRFOutputsJSON;
+}
+
 interface AuthenticationExtensionsLargeBlobInputs {
     read?: boolean;
     support?: string;
@@ -233,6 +241,12 @@ interface AuthenticationExtensionsLargeBlobOutputs {
     written?: boolean;
 }
 
+interface AuthenticationExtensionsLargeBlobOutputsJSON {
+    blob?: Base64URLString;
+    supported?: boolean;
+    written?: boolean;
+}
+
 interface AuthenticationExtensionsPRFInputs {
     eval?: AuthenticationExtensionsPRFValues;
     evalByCredential?: Record<string, AuthenticationExtensionsPRFValues>;
@@ -248,6 +262,11 @@ interface AuthenticationExtensionsPRFOutputs {
     results?: AuthenticationExtensionsPRFValues;
 }
 
+interface AuthenticationExtensionsPRFOutputsJSON {
+    enabled?: boolean;
+    results?: AuthenticationExtensionsPRFValuesJSON;
+}
+
 interface AuthenticationExtensionsPRFValues {
     first: BufferSource;
     second?: BufferSource;
@@ -258,6 +277,31 @@ interface AuthenticationExtensionsPRFValuesJSON {
     second?: Base64URLString;
 }
 
+interface AuthenticationResponseJSON {
+    authenticatorAttachment?: string;
+    clientExtensionResults: AuthenticationExtensionsClientOutputsJSON;
+    id: string;
+    rawId: Base64URLString;
+    response: AuthenticatorAssertionResponseJSON;
+    type: string;
+}
+
+interface AuthenticatorAssertionResponseJSON {
+    authenticatorData: Base64URLString;
+    clientDataJSON: Base64URLString;
+    signature: Base64URLString;
+    userHandle?: Base64URLString;
+}
+
+interface AuthenticatorAttestationResponseJSON {
+    attestationObject: Base64URLString;
+    authenticatorData: Base64URLString;
+    clientDataJSON: Base64URLString;
+    publicKey?: Base64URLString;
+    publicKeyAlgorithm: COSEAlgorithmIdentifier;
+    transports: string[];
+}
+
 interface AuthenticatorSelectionCriteria {
     authenticatorAttachment?: AuthenticatorAttachment;
     requireResidentKey?: boolean;
@@ -2098,6 +2142,15 @@ interface RegistrationOptions {
     updateViaCache?: ServiceWorkerUpdateViaCache;
 }
 
+interface RegistrationResponseJSON {
+    authenticatorAttachment?: string;
+    clientExtensionResults: AuthenticationExtensionsClientOutputsJSON;
+    id: string;
+    rawId: Base64URLString;
+    response: AuthenticatorAttestationResponseJSON;
+    type: string;
+}
+
 interface Report {
     body?: ReportBody | null;
     type?: string;
@@ -26953,7 +27006,7 @@ interface PublicKeyCredential extends Credential {
      *
      * [MDN Reference](https://developer.mozilla.org/docs/Web/API/PublicKeyCredential/toJSON)
      */
-    toJSON(): PublicKeyCredentialJSON;
+    toJSON(): RegistrationResponseJSON | AuthenticationResponseJSON;
 }
 
 declare var PublicKeyCredential: {
@@ -42398,7 +42451,6 @@ type OptionalPostfixToken<T extends string> = ` ${T}` | "";
 type OptionalPrefixToken<T extends string> = `${T} ` | "";
 type PerformanceEntryList = PerformanceEntry[];
 type PublicKeyCredentialClientCapabilities = Record<string, boolean>;
-type PublicKeyCredentialJSON = any;
 type RTCRtpTransform = RTCRtpScriptTransform;
 type ReadableStreamController<T> = ReadableStreamDefaultController<T> | ReadableByteStreamController;
 type ReadableStreamReadResult<T> = ReadableStreamReadValueResult<T> | ReadableStreamReadDoneResult<T>;
diff --git a/baselines/ts5.5/dom.generated.d.ts b/baselines/ts5.5/dom.generated.d.ts
index 308ad8250..ee561fd85 100644
--- a/baselines/ts5.5/dom.generated.d.ts
+++ b/baselines/ts5.5/dom.generated.d.ts
@@ -212,6 +212,14 @@ interface AuthenticationExtensionsClientOutputs {
     prf?: AuthenticationExtensionsPRFOutputs;
 }
 
+interface AuthenticationExtensionsClientOutputsJSON {
+    appid?: boolean;
+    appidExclude?: boolean;
+    credProps?: CredentialPropertiesOutput;
+    largeBlob?: AuthenticationExtensionsLargeBlobOutputsJSON;
+    prf?: AuthenticationExtensionsPRFOutputsJSON;
+}
+
 interface AuthenticationExtensionsLargeBlobInputs {
     read?: boolean;
     support?: string;
@@ -230,6 +238,12 @@ interface AuthenticationExtensionsLargeBlobOutputs {
     written?: boolean;
 }
 
+interface AuthenticationExtensionsLargeBlobOutputsJSON {
+    blob?: Base64URLString;
+    supported?: boolean;
+    written?: boolean;
+}
+
 interface AuthenticationExtensionsPRFInputs {
     eval?: AuthenticationExtensionsPRFValues;
     evalByCredential?: Record<string, AuthenticationExtensionsPRFValues>;
@@ -245,6 +259,11 @@ interface AuthenticationExtensionsPRFOutputs {
     results?: AuthenticationExtensionsPRFValues;
 }
 
+interface AuthenticationExtensionsPRFOutputsJSON {
+    enabled?: boolean;
+    results?: AuthenticationExtensionsPRFValuesJSON;
+}
+
 interface AuthenticationExtensionsPRFValues {
     first: BufferSource;
     second?: BufferSource;
@@ -255,6 +274,31 @@ interface AuthenticationExtensionsPRFValuesJSON {
     second?: Base64URLString;
 }
 
+interface AuthenticationResponseJSON {
+    authenticatorAttachment?: string;
+    clientExtensionResults: AuthenticationExtensionsClientOutputsJSON;
+    id: string;
+    rawId: Base64URLString;
+    response: AuthenticatorAssertionResponseJSON;
+    type: string;
+}
+
+interface AuthenticatorAssertionResponseJSON {
+    authenticatorData: Base64URLString;
+    clientDataJSON: Base64URLString;
+    signature: Base64URLString;
+    userHandle?: Base64URLString;
+}
+
+interface AuthenticatorAttestationResponseJSON {
+    attestationObject: Base64URLString;
+    authenticatorData: Base64URLString;
+    clientDataJSON: Base64URLString;
+    publicKey?: Base64URLString;
+    publicKeyAlgorithm: COSEAlgorithmIdentifier;
+    transports: string[];
+}
+
 interface AuthenticatorSelectionCriteria {
     authenticatorAttachment?: AuthenticatorAttachment;
     requireResidentKey?: boolean;
@@ -2095,6 +2139,15 @@ interface RegistrationOptions {
     updateViaCache?: ServiceWorkerUpdateViaCache;
 }
 
+interface RegistrationResponseJSON {
+    authenticatorAttachment?: string;
+    clientExtensionResults: AuthenticationExtensionsClientOutputsJSON;
+    id: string;
+    rawId: Base64URLString;
+    response: AuthenticatorAttestationResponseJSON;
+    type: string;
+}
+
 interface Report {
     body?: ReportBody | null;
     type?: string;
@@ -26929,7 +26982,7 @@ interface PublicKeyCredential extends Credential {
      *
      * [MDN Reference](https://developer.mozilla.org/docs/Web/API/PublicKeyCredential/toJSON)
      */
-    toJSON(): PublicKeyCredentialJSON;
+    toJSON(): RegistrationResponseJSON | AuthenticationResponseJSON;
 }
 
 declare var PublicKeyCredential: {
@@ -42372,7 +42425,6 @@ type OptionalPostfixToken<T extends string> = ` ${T}` | "";
 type OptionalPrefixToken<T extends string> = `${T} ` | "";
 type PerformanceEntryList = PerformanceEntry[];
 type PublicKeyCredentialClientCapabilities = Record<string, boolean>;
-type PublicKeyCredentialJSON = any;
 type RTCRtpTransform = RTCRtpScriptTransform;
 type ReadableStreamController<T> = ReadableStreamDefaultController<T> | ReadableByteStreamController;
 type ReadableStreamReadResult<T> = ReadableStreamReadValueResult<T> | ReadableStreamReadDoneResult<T>;
diff --git a/baselines/ts5.6/dom.generated.d.ts b/baselines/ts5.6/dom.generated.d.ts
index 3d8546117..08c30221b 100644
--- a/baselines/ts5.6/dom.generated.d.ts
+++ b/baselines/ts5.6/dom.generated.d.ts
@@ -212,6 +212,14 @@ interface AuthenticationExtensionsClientOutputs {
     prf?: AuthenticationExtensionsPRFOutputs;
 }
 
+interface AuthenticationExtensionsClientOutputsJSON {
+    appid?: boolean;
+    appidExclude?: boolean;
+    credProps?: CredentialPropertiesOutput;
+    largeBlob?: AuthenticationExtensionsLargeBlobOutputsJSON;
+    prf?: AuthenticationExtensionsPRFOutputsJSON;
+}
+
 interface AuthenticationExtensionsLargeBlobInputs {
     read?: boolean;
     support?: string;
@@ -230,6 +238,12 @@ interface AuthenticationExtensionsLargeBlobOutputs {
     written?: boolean;
 }
 
+interface AuthenticationExtensionsLargeBlobOutputsJSON {
+    blob?: Base64URLString;
+    supported?: boolean;
+    written?: boolean;
+}
+
 interface AuthenticationExtensionsPRFInputs {
     eval?: AuthenticationExtensionsPRFValues;
     evalByCredential?: Record<string, AuthenticationExtensionsPRFValues>;
@@ -245,6 +259,11 @@ interface AuthenticationExtensionsPRFOutputs {
     results?: AuthenticationExtensionsPRFValues;
 }
 
+interface AuthenticationExtensionsPRFOutputsJSON {
+    enabled?: boolean;
+    results?: AuthenticationExtensionsPRFValuesJSON;
+}
+
 interface AuthenticationExtensionsPRFValues {
     first: BufferSource;
     second?: BufferSource;
@@ -255,6 +274,31 @@ interface AuthenticationExtensionsPRFValuesJSON {
     second?: Base64URLString;
 }
 
+interface AuthenticationResponseJSON {
+    authenticatorAttachment?: string;
+    clientExtensionResults: AuthenticationExtensionsClientOutputsJSON;
+    id: string;
+    rawId: Base64URLString;
+    response: AuthenticatorAssertionResponseJSON;
+    type: string;
+}
+
+interface AuthenticatorAssertionResponseJSON {
+    authenticatorData: Base64URLString;
+    clientDataJSON: Base64URLString;
+    signature: Base64URLString;
+    userHandle?: Base64URLString;
+}
+
+interface AuthenticatorAttestationResponseJSON {
+    attestationObject: Base64URLString;
+    authenticatorData: Base64URLString;
+    clientDataJSON: Base64URLString;
+    publicKey?: Base64URLString;
+    publicKeyAlgorithm: COSEAlgorithmIdentifier;
+    transports: string[];
+}
+
 interface AuthenticatorSelectionCriteria {
     authenticatorAttachment?: AuthenticatorAttachment;
     requireResidentKey?: boolean;
@@ -2095,6 +2139,15 @@ interface RegistrationOptions {
     updateViaCache?: ServiceWorkerUpdateViaCache;
 }
 
+interface RegistrationResponseJSON {
+    authenticatorAttachment?: string;
+    clientExtensionResults: AuthenticationExtensionsClientOutputsJSON;
+    id: string;
+    rawId: Base64URLString;
+    response: AuthenticatorAttestationResponseJSON;
+    type: string;
+}
+
 interface Report {
     body?: ReportBody | null;
     type?: string;
@@ -26950,7 +27003,7 @@ interface PublicKeyCredential extends Credential {
      *
      * [MDN Reference](https://developer.mozilla.org/docs/Web/API/PublicKeyCredential/toJSON)
      */
-    toJSON(): PublicKeyCredentialJSON;
+    toJSON(): RegistrationResponseJSON | AuthenticationResponseJSON;
 }
 
 declare var PublicKeyCredential: {
@@ -42395,7 +42448,6 @@ type OptionalPostfixToken<T extends string> = ` ${T}` | "";
 type OptionalPrefixToken<T extends string> = `${T} ` | "";
 type PerformanceEntryList = PerformanceEntry[];
 type PublicKeyCredentialClientCapabilities = Record<string, boolean>;
-type PublicKeyCredentialJSON = any;
 type RTCRtpTransform = RTCRtpScriptTransform;
 type ReadableStreamController<T> = ReadableStreamDefaultController<T> | ReadableByteStreamController;
 type ReadableStreamReadResult<T> = ReadableStreamReadValueResult<T> | ReadableStreamReadDoneResult<T>;
diff --git a/baselines/ts5.9/dom.generated.d.ts b/baselines/ts5.9/dom.generated.d.ts
index 01b293947..d4a02a001 100644
--- a/baselines/ts5.9/dom.generated.d.ts
+++ b/baselines/ts5.9/dom.generated.d.ts
@@ -212,6 +212,14 @@ interface AuthenticationExtensionsClientOutputs {
     prf?: AuthenticationExtensionsPRFOutputs;
 }
 
+interface AuthenticationExtensionsClientOutputsJSON {
+    appid?: boolean;
+    appidExclude?: boolean;
+    credProps?: CredentialPropertiesOutput;
+    largeBlob?: AuthenticationExtensionsLargeBlobOutputsJSON;
+    prf?: AuthenticationExtensionsPRFOutputsJSON;
+}
+
 interface AuthenticationExtensionsLargeBlobInputs {
     read?: boolean;
     support?: string;
@@ -230,6 +238,12 @@ interface AuthenticationExtensionsLargeBlobOutputs {
     written?: boolean;
 }
 
+interface AuthenticationExtensionsLargeBlobOutputsJSON {
+    blob?: Base64URLString;
+    supported?: boolean;
+    written?: boolean;
+}
+
 interface AuthenticationExtensionsPRFInputs {
     eval?: AuthenticationExtensionsPRFValues;
     evalByCredential?: Record<string, AuthenticationExtensionsPRFValues>;
@@ -245,6 +259,11 @@ interface AuthenticationExtensionsPRFOutputs {
     results?: AuthenticationExtensionsPRFValues;
 }
 
+interface AuthenticationExtensionsPRFOutputsJSON {
+    enabled?: boolean;
+    results?: AuthenticationExtensionsPRFValuesJSON;
+}
+
 interface AuthenticationExtensionsPRFValues {
     first: BufferSource;
     second?: BufferSource;
@@ -255,6 +274,31 @@ interface AuthenticationExtensionsPRFValuesJSON {
     second?: Base64URLString;
 }
 
+interface AuthenticationResponseJSON {
+    authenticatorAttachment?: string;
+    clientExtensionResults: AuthenticationExtensionsClientOutputsJSON;
+    id: string;
+    rawId: Base64URLString;
+    response: AuthenticatorAssertionResponseJSON;
+    type: string;
+}
+
+interface AuthenticatorAssertionResponseJSON {
+    authenticatorData: Base64URLString;
+    clientDataJSON: Base64URLString;
+    signature: Base64URLString;
+    userHandle?: Base64URLString;
+}
+
+interface AuthenticatorAttestationResponseJSON {
+    attestationObject: Base64URLString;
+    authenticatorData: Base64URLString;
+    clientDataJSON: Base64URLString;
+    publicKey?: Base64URLString;
+    publicKeyAlgorithm: COSEAlgorithmIdentifier;
+    transports: string[];
+}
+
 interface AuthenticatorSelectionCriteria {
     authenticatorAttachment?: AuthenticatorAttachment;
     requireResidentKey?: boolean;
@@ -2095,6 +2139,15 @@ interface RegistrationOptions {
     updateViaCache?: ServiceWorkerUpdateViaCache;
 }
 
+interface RegistrationResponseJSON {
+    authenticatorAttachment?: string;
+    clientExtensionResults: AuthenticationExtensionsClientOutputsJSON;
+    id: string;
+    rawId: Base64URLString;
+    response: AuthenticatorAttestationResponseJSON;
+    type: string;
+}
+
 interface Report {
     body?: ReportBody | null;
     type?: string;
@@ -26950,7 +27003,7 @@ interface PublicKeyCredential extends Credential {
      *
      * [MDN Reference](https://developer.mozilla.org/docs/Web/API/PublicKeyCredential/toJSON)
      */
-    toJSON(): PublicKeyCredentialJSON;
+    toJSON(): RegistrationResponseJSON | AuthenticationResponseJSON;
 }
 
 declare var PublicKeyCredential: {
@@ -42395,7 +42448,6 @@ type OptionalPostfixToken<T extends string> = ` ${T}` | "";
 type OptionalPrefixToken<T extends string> = `${T} ` | "";
 type PerformanceEntryList = PerformanceEntry[];
 type PublicKeyCredentialClientCapabilities = Record<string, boolean>;
-type PublicKeyCredentialJSON = any;
 type RTCRtpTransform = RTCRtpScriptTransform;
 type ReadableStreamController<T> = ReadableStreamDefaultController<T> | ReadableByteStreamController;
 type ReadableStreamReadResult<T> = ReadableStreamReadValueResult<T> | ReadableStreamReadDoneResult<T>;
diff --git a/inputfiles/patches/webauthn.kdl b/inputfiles/patches/webauthn.kdl
index f2f166e3d..14e8374e7 100644
--- a/inputfiles/patches/webauthn.kdl
+++ b/inputfiles/patches/webauthn.kdl
@@ -1,3 +1,10 @@
+interface PublicKeyCredential {
+  method toJSON signatureIndex=0 {
+    type RegistrationResponseJSON
+    type AuthenticationResponseJSON
+  }
+}
+
 removals {
   enum AuthenticatorTransport {
     smart-card // WebKit only as of 2023-05
diff --git a/src/build/patches.ts b/src/build/patches.ts
index 26368e585..b560b5174 100644
--- a/src/build/patches.ts
+++ b/src/build/patches.ts
@@ -48,13 +48,13 @@ function string(arg: unknown): string {
   return arg;
 }
 
-function handleTyped(type: Node): DeepPartial<Typed> {
+function handleSingleTypeNode(type: Node): DeepPartial<Typed> {
   const isTyped = type.name == "type";
   if (!isTyped) {
     throw new Error("Expected a type node");
   }
   const subType =
-    type.children.length > 0 ? handleTyped(type.children[0]) : undefined;
+    type.children.length > 0 ? handleTyped(type.children) : undefined;
   return {
     ...optionalMember("type", "string", type.values[0]),
     subtype: subType,
@@ -62,6 +62,28 @@ function handleTyped(type: Node): DeepPartial<Typed> {
   };
 }
 
+function handleTyped(
+  typeNodes: Node[],
+  returns?: Value,
+): DeepPartial<Typed> | undefined {
+  // Support multiple types, merged into array. If only one, keep as object.
+  let type: DeepPartial<Typed> | undefined;
+  if (typeNodes.length === 1) {
+    type = handleSingleTypeNode(typeNodes[0]);
+  } else if (typeNodes.length > 1) {
+    const types = typeNodes.map(handleSingleTypeNode);
+    type = { type: types };
+  } else if (returns) {
+    type = {
+      type: string(returns),
+      subtype: undefined,
+    };
+  } else {
+    type = undefined;
+  }
+  return type;
+}
+
 function handleTypeParameters(value: Value | Node) {
   if (!value) {
     return {};
@@ -246,22 +268,14 @@ function handleEvent(child: Node): Event {
  * @param child The child node to handle.
  */
 function handleProperty(child: Node): DeepPartial<Property> {
-  let typeNode: Node | undefined;
-  for (const c of child.children) {
-    if (c.name === "type") {
-      typeNode = c;
-      break;
-    }
-  }
+  const typeNodes = child.children.filter((c) => c.name === "type");
 
   return {
     name: string(child.values[0]),
     ...optionalMember("exposed", "string", child.properties?.exposed),
     ...optionalMember("optional", "boolean", child.properties?.optional),
     ...optionalMember("overrideType", "string", child.properties?.overrideType),
-    ...(typeNode
-      ? handleTyped(typeNode)
-      : optionalMember("type", "string", child.properties?.type)),
+    ...handleTyped(typeNodes, child.properties?.type),
     ...optionalMember("readonly", "boolean", child.properties?.readonly),
     ...optionalMember("deprecated", "string", child.properties?.deprecated),
   };
@@ -300,16 +314,14 @@ function handleParam(node: Node) {
 function handleMethod(child: Node): DeepPartial<OverridableMethod> {
   const name = string(child.values[0]);
 
-  let typeNode: Node | undefined;
+  // Collect all type nodes into an array
+  const typeNodes: Node[] = [];
   const params: Partial<Param>[] = [];
 
   for (const c of child.children) {
     switch (c.name) {
       case "type":
-        if (typeNode) {
-          throw new Error(`Method "${name}" has multiple type nodes (invalid)`);
-        }
-        typeNode = c;
+        typeNodes.push(c);
         break;
 
       case "param":
@@ -321,16 +333,8 @@ function handleMethod(child: Node): DeepPartial<OverridableMethod> {
     }
   }
 
-  const type = typeNode
-    ? handleTyped(typeNode)
-    : child.properties?.returns
-      ? {
-          type: string(child.properties?.returns),
-          subtype: undefined,
-        }
-      : null;
-
   const signatureIndex = child.properties?.signatureIndex;
+  const type = handleTyped(typeNodes, child.properties?.returns);
 
   let signature: OverridableMethod["signature"] = [];
   if (type || params.length > 0) {