diff --git a/inputfiles/addedTypes.jsonc b/inputfiles/addedTypes.jsonc
index 9260d0783..bfa25c385 100644
--- a/inputfiles/addedTypes.jsonc
+++ b/inputfiles/addedTypes.jsonc
@@ -511,24 +511,6 @@
                 "name": "EventListenerOrEventListenerObject",
                 "overrideType": "EventListener | EventListenerObject"
             },
-            {
-                "name": "OptionalPrefixToken",
-                "typeParameters": [
-                    {
-                        "name": "T extends string"
-                    }
-                ],
-                "overrideType": "`${T} ` | \"\""
-            },
-            {
-                "name": "OptionalPostfixToken",
-                "typeParameters": [
-                    {
-                        "name": "T extends string"
-                    }
-                ],
-                "overrideType": "` ${T}` | \"\""
-            },
             {
                 "name": "AutoFillSection",
                 // Note: this will also eagerly match any invalid string
diff --git a/inputfiles/patches/html-autocomplete.kdl b/inputfiles/patches/html-autocomplete.kdl
index a73f49aac..986541bcb 100644
--- a/inputfiles/patches/html-autocomplete.kdl
+++ b/inputfiles/patches/html-autocomplete.kdl
@@ -72,3 +72,11 @@ enum AutoFillContactField {
 enum AutoFillCredentialField {
   webauthn
 }
+
+typedef OptionalPrefixToken overrideType=#"`${T} ` | """# {
+  typeParameters T extends=string
+}
+
+typedef OptionalPostfixToken overrideType=#"` ${T}` | """# {
+  typeParameters T extends=string
+}
diff --git a/src/build/patches.ts b/src/build/patches.ts
index f2484e436..ec9fa5954 100644
--- a/src/build/patches.ts
+++ b/src/build/patches.ts
@@ -104,6 +104,7 @@ function handleTypeParameters(value: Value | Node) {
       {
         name: string(node.values[0]),
         ...optionalMember("default", "string", node.properties?.default),
+        ...optionalMember("extends", "string", node.properties?.extends),
       },
     ],
   };
@@ -448,7 +449,23 @@ function handleMember(c: Node): DeepPartial<Member> {
  * @param node The typedef node to handle.
  */
 function handleTypedef(node: Node): DeepPartial<TypeDef> {
-  const typeNodes = node.children.filter((c) => c.name === "type");
+  const typeNodes: Node[] = [];
+  let typeParameters = {};
+  for (const child of node.children) {
+    switch (child.name) {
+      case "type":
+        typeNodes.push(child);
+        break;
+      case "typeParameters": {
+        typeParameters = handleTypeParameters(child);
+        break;
+      }
+      default:
+        throw new Error(
+          `Unexpected child "${child.name}" in typedef "${node.values[0]}"`,
+        );
+    }
+  }
   return {
     name: string(node.values[0]),
     ...handleTyped(typeNodes),
@@ -458,6 +475,7 @@ function handleTypedef(node: Node): DeepPartial<TypeDef> {
       node.properties?.legacyNamespace,
     ),
     ...optionalMember("overrideType", "string", node.properties?.overrideType),
+    ...typeParameters,
   };
 }