diff --git a/src/decorate.ts b/src/decorate.ts
index 1c9b3ba..82681bd 100644
--- a/src/decorate.ts
+++ b/src/decorate.ts
@@ -25,9 +25,7 @@
 import { getIntegration } from '@/global';
 import { applyClassMixins } from '@/util';
 import { define } from '@/auto';
-import { DecoratorOptionType, DecoratorDescriptorType } from './interfaces';
-
-type Constructor = new (...args: unknown[]) => object;
+import { DecoratorOptionType, DecoratorDescriptorType, Constructor } from './interfaces';
 
 const itemMap = new WeakMap<object, Set<string>>();
 
diff --git a/src/interfaces.ts b/src/interfaces.ts
index 32f7c4d..76bd4cc 100644
--- a/src/interfaces.ts
+++ b/src/interfaces.ts
@@ -136,6 +136,20 @@ export interface IntegrationOptions {
  * };
  * ```
  */
+/**
+ * A class constructor type that produces instances of type T.
+ *
+ * Unlike a simple `new (...args) => T` signature, this type also
+ * captures that constructors have a `prototype` property, which is
+ * important for mixin and class composition utilities.
+ *
+ * @typeParam T - The instance type that the constructor creates
+ */
+export type Constructor<T = object> = {
+  new (...args: unknown[]): T,
+  prototype: T,
+};
+
 export interface Integration {
   /**
    * Defines a reactive property on an object.
diff --git a/src/util.ts b/src/util.ts
index 8b08b9b..82b75a4 100644
--- a/src/util.ts
+++ b/src/util.ts
@@ -7,6 +7,8 @@
  * allowing you to build complex objects from simpler pieces.
  */
 
+import type { Constructor } from '@/interfaces';
+
 type AnyObject = Record<string, unknown>;
 
 type OptionalPropertyNames<T> = {
@@ -94,8 +96,6 @@ export function merge<A extends ObjectOrFactory[]>(...types: [...A]): Spread<A>
   return newVal as Spread<A>;
 }
 
-type Constructor = new (...args: unknown[]) => object;
-
 /**
  * Applies mixin classes to a base class by merging their prototypes.
  *