src/ZodSchemaClass.ts

@@ -17,19 +17,6 @@ export class ZodSchemaClassBuilder<
 extends TraitExpressionBuilder<Superclass, Traits> {
     declare ["constructor"]: typeof ZodSchemaClassBuilder
 
-    extends<
-        Super extends AbstractClass<object>
-    >(
-        //                                        \/ Ensures `extends` can only be called once at the beginning
-        this:        ZodSchemaClassBuilder<typeof TraitExpression.NullSuperclass, Traits>,
-        superclass:  Super,
-    ) {
-        return new this.constructor(
-            superclass,
-            this.expressionTraits,
-        )
-    }
-
     schema<
         Superclass        extends AbstractClass<object, []> & { schema?: never, defaultValues?: never },
 
@@ -147,6 +134,14 @@ export interface ZodSchemaClassBuilder<
     Superclass extends AbstractClass<object>,
     Traits     extends readonly Trait<any, any, any, any>[],
 > {
+    extends<
+        Super extends AbstractClass<object>
+    >(
+        //                                        \/ Ensures `extends` can only be called once at the beginning
+        this:        ZodSchemaClassBuilder<typeof TraitExpression.NullSuperclass, Traits>,
+        superclass:  Super,
+    ): InstanceType<typeof this.constructor<Super, Traits>>
+
     expresses<
         const T extends readonly Trait<
             TraitExpression<

src/tests.ts

@@ -7,6 +7,7 @@ import { AbstractClass, Class } from "type-fest"
 
 
 const exp = new ZodSchemaClassBuilder(TraitExpression.NullSuperclass, [])
+    .extends(class {})
     .schema({
         schema: z.object({
             /** User ID */