diff --git a/packages/@aws-cdk/aws-cognito/lib/user-pool.ts b/packages/@aws-cdk/aws-cognito/lib/user-pool.ts
index 6277ee0f467ee..adc3f51bf37a2 100644
--- a/packages/@aws-cdk/aws-cognito/lib/user-pool.ts
+++ b/packages/@aws-cdk/aws-cognito/lib/user-pool.ts
@@ -830,7 +830,7 @@ export class UserPool extends UserPoolBase {
    */
   public addTrigger(operation: UserPoolOperation, fn: lambda.IFunction): void {
     if (operation.operationName in this.triggers) {
-      throw new Error(`A trigger for the operation ${operation} already exists.`);
+      throw new Error(`A trigger for the operation ${operation.operationName} already exists.`);
     }
 
     this.addLambdaPermission(fn, operation.operationName);
diff --git a/packages/@aws-cdk/aws-cognito/test/user-pool.test.ts b/packages/@aws-cdk/aws-cognito/test/user-pool.test.ts
index 7b132803da2d6..5aa6c48ee99fc 100644
--- a/packages/@aws-cdk/aws-cognito/test/user-pool.test.ts
+++ b/packages/@aws-cdk/aws-cognito/test/user-pool.test.ts
@@ -403,7 +403,7 @@ describe('User Pool', () => {
 
     // WHEN
     userpool.addTrigger(UserPoolOperation.CREATE_AUTH_CHALLENGE, fn1);
-    expect(() => userpool.addTrigger(UserPoolOperation.CREATE_AUTH_CHALLENGE, fn2)).toThrow(/already exists/);
+    expect(() => userpool.addTrigger(UserPoolOperation.CREATE_AUTH_CHALLENGE, fn2)).toThrow(/createAuthChallenge already exists/);
   });
 
   test('no username aliases specified', () => {