diff --git a/packages/frontend-internal/src/wiring/OpaqueType.ts b/packages/frontend-internal/src/wiring/OpaqueType.ts
index abd74bd910..3d05b619bc 100644
--- a/packages/frontend-internal/src/wiring/OpaqueType.ts
+++ b/packages/frontend-internal/src/wiring/OpaqueType.ts
@@ -122,7 +122,10 @@ export class OpaqueType<
    * @param value The remaining public and internal properties of the instance
    * @returns An instance of the opaque type
    */
-  createInstance<TVersion extends T['versions']['version']>(
+  createInstance<
+    TVersion extends T['versions']['version'],
+    TPublic extends T['public'],
+  >(
     version: TVersion,
     props: Omit<T['public'], '$$type'> &
       (T['versions'] extends infer UVersion
@@ -131,12 +134,12 @@ export class OpaqueType<
           : never
         : never) &
       Object, // & Object to allow for object properties too, e.g. toString()
-  ): T['public'] {
+  ): TPublic {
     return {
       ...(props as object),
       $$type: this.#type,
       ...(version && { version }),
-    } as T['public'];
+    } as unknown as TPublic;
   }
 
   #isThisInternalType(value: unknown): value is T['public'] & T['versions'] {
diff --git a/packages/frontend-plugin-api/src/wiring/createExtension.ts b/packages/frontend-plugin-api/src/wiring/createExtension.ts
index 4941324bed..ac7b1de432 100644
--- a/packages/frontend-plugin-api/src/wiring/createExtension.ts
+++ b/packages/frontend-plugin-api/src/wiring/createExtension.ts
@@ -366,26 +366,6 @@ export function createExtension<
   namespace: string | undefined extends TNamespace ? undefined : TNamespace;
   name: string | undefined extends TName ? undefined : TName;
 }> {
-  type T = {
-    config: string extends keyof TConfigSchema
-      ? {}
-      : {
-          [key in keyof TConfigSchema]: z.infer<ReturnType<TConfigSchema[key]>>;
-        };
-    configInput: string extends keyof TConfigSchema
-      ? {}
-      : z.input<
-          z.ZodObject<{
-            [key in keyof TConfigSchema]: ReturnType<TConfigSchema[key]>;
-          }>
-        >;
-    output: UOutput;
-    inputs: TInputs;
-    kind: string | undefined extends TKind ? undefined : TKind;
-    namespace: string | undefined extends TNamespace ? undefined : TNamespace;
-    name: string | undefined extends TName ? undefined : TName;
-  };
-
   const schemaDeclaration = options.config?.schema;
   const configSchema =
     schemaDeclaration &&
@@ -398,7 +378,27 @@ export function createExtension<
     );
 
   return OpaqueExtensionDefinition.createInstance('v2', {
-    T: undefined as unknown as T,
+    T: undefined as unknown as {
+      config: string extends keyof TConfigSchema
+        ? {}
+        : {
+            [key in keyof TConfigSchema]: z.infer<
+              ReturnType<TConfigSchema[key]>
+            >;
+          };
+      configInput: string extends keyof TConfigSchema
+        ? {}
+        : z.input<
+            z.ZodObject<{
+              [key in keyof TConfigSchema]: ReturnType<TConfigSchema[key]>;
+            }>
+          >;
+      output: UOutput;
+      inputs: TInputs;
+      kind: string | undefined extends TKind ? undefined : TKind;
+      namespace: string | undefined extends TNamespace ? undefined : TNamespace;
+      name: string | undefined extends TName ? undefined : TName;
+    },
     kind: options.kind,
     namespace: options.namespace,
     name: options.name,
@@ -510,5 +510,5 @@ export function createExtension<
         },
       }) as ExtensionDefinition<any>;
     },
-  }) as ExtensionDefinition<T>;
+  });
 }