diff --git a/inputfiles/addedTypes.jsonc b/inputfiles/addedTypes.jsonc
index da2e10e3a..bfdf350ce 100644
--- a/inputfiles/addedTypes.jsonc
+++ b/inputfiles/addedTypes.jsonc
@@ -446,10 +446,6 @@
                 "additionalTypes": ["Headers"],
                 "name": "HeadersInit"
             },
-            {
-                "overrideType": "number | string | Date | BufferSource | IDBValidKey[]",
-                "name": "IDBValidKey"
-            },
             {
                 "type": {
                     "0": {
@@ -489,11 +485,6 @@
                     }
                 ]
             },
-            {
-                "name": "ImportValue",
-                "legacyNamespace": "WebAssembly",
-                "overrideType": "ExportValue | number"
-            },
             {
                 "name": "ModuleImports",
                 "legacyNamespace": "WebAssembly",
diff --git a/inputfiles/patches/indexeddb.kdl b/inputfiles/patches/indexeddb.kdl
index ee4b5e222..02a0fba2d 100644
--- a/inputfiles/patches/indexeddb.kdl
+++ b/inputfiles/patches/indexeddb.kdl
@@ -7,3 +7,13 @@ interface IDBRequest {
 }
 
 interface IDBOpenDBRequest extends=IDBRequest<IDBDatabase>
+
+typedef IDBValidKey {
+   type long
+   type DOMString
+   type Date
+   type BufferSource
+   type sequence {
+      type IDBValidKey
+   }
+}
diff --git a/inputfiles/patches/webassembly.kdl b/inputfiles/patches/webassembly.kdl
index 426530070..c3adceb31 100644
--- a/inputfiles/patches/webassembly.kdl
+++ b/inputfiles/patches/webassembly.kdl
@@ -16,6 +16,11 @@ dictionary MemoryDescriptor {
   member shared type=boolean
 }
 
+typedef ImportValue legacyNamespace=WebAssembly {
+  type ExportValue
+  type long
+}
+
 removals {
   // Overridden with `keyof ValueTypeMap`
   enum ValueType
diff --git a/src/build/patches.ts b/src/build/patches.ts
index a2515c73f..54ab46911 100644
--- a/src/build/patches.ts
+++ b/src/build/patches.ts
@@ -16,6 +16,7 @@ import type {
   Dictionary,
   Member,
   Signature,
+  TypeDef,
 } from "./types.js";
 import { readdir, readFile } from "fs/promises";
 import { merge } from "./helpers.js";
@@ -120,6 +121,7 @@ function convertKDLNodes(nodes: Node[]): DeepPartial<WebIdl> {
   const mixin: Record<string, DeepPartial<Interface>> = {};
   const interfaces: Record<string, DeepPartial<Interface>> = {};
   const dictionary: Record<string, DeepPartial<Dictionary>> = {};
+  const typedefs: DeepPartial<TypeDef>[] = [];
 
   for (const node of nodes) {
     // Note: no "removals" handling here; caller is responsible for splitting
@@ -143,6 +145,9 @@ function convertKDLNodes(nodes: Node[]): DeepPartial<WebIdl> {
       case "dictionary":
         dictionary[name] = merge(dictionary[name], handleDictionary(node));
         break;
+      case "typedef":
+        typedefs.push(handleTypeDef(node));
+        break;
       default:
         throw new Error(`Unknown node name: ${node.name}`);
     }
@@ -155,6 +160,7 @@ function convertKDLNodes(nodes: Node[]): DeepPartial<WebIdl> {
       interface: interfaces,
     }),
     ...optionalNestedMember("dictionaries", dictionary, { dictionary }),
+    ...optionalNestedMember("typedefs", typedefs, { typedef: typedefs }),
   };
 }
 
@@ -432,6 +438,23 @@ function handleMember(c: Node): DeepPartial<Member> {
   };
 }
 
+/**
+ * Handles type definition nodes
+ * @param node The type definition node to handle.
+ */
+function handleTypeDef(node: Node): DeepPartial<TypeDef> {
+  const typeNodes = node.children.filter((c) => c.name === "type");
+  return {
+    name: string(node.values[0]),
+    ...handleTyped(typeNodes),
+    ...optionalMember(
+      "legacyNamespace",
+      "string",
+      node.properties?.legacyNamespace,
+    ),
+  };
+}
+
 /**
  * Collect all file URLs in a directory.
  */