diff --git a/src/index.ts b/src/index.ts
index 00e79302a..2bdce99af 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -43,7 +43,7 @@ function addMethod<T extends ISchema<any>>(
   name: string,
   fn: (this: T, ...args: any[]) => T,
 ): void;
-function addMethod<T extends new (...args: any) => ISchema<any>>(
+function addMethod<T extends abstract new (...args: any) => ISchema<any>>(
   schemaType: T,
   name: string,
   fn: (this: InstanceType<T>, ...args: any[]) => InstanceType<T>,
diff --git a/test/types/types.ts b/test/types/types.ts
index 8a27b49a5..30960acec 100644
--- a/test/types/types.ts
+++ b/test/types/types.ts
@@ -10,6 +10,7 @@ import {
   bool,
   reach,
   addMethod,
+  Schema,
 } from '../../src';
 import { create as tuple } from '../../src/tuple';
 import { create as lazy } from '../../src/Lazy';
@@ -1079,6 +1080,10 @@ reach: {
 }
 
 addMethod: {
+  addMethod(Schema, 'foo', function () {
+    return this.clone();
+  });
+
   addMethod(string, 'foo', function () {
     return this.clone();
   });