diff --git a/clients/client-acm/src/ACMClient.ts b/clients/client-acm/src/ACMClient.ts
index 5e6f066d4eeee..8a26013e4f56f 100644
--- a/clients/client-acm/src/ACMClient.ts
+++ b/clients/client-acm/src/ACMClient.ts
@@ -33,6 +33,7 @@ import {
 } from "@smithy/smithy-client";
 import {
   BodyLengthCalculator as __BodyLengthCalculator,
+  CheckOptionalClientConfig as __CheckOptionalClientConfig,
   Checksum as __Checksum,
   ChecksumConstructor as __ChecksumConstructor,
   Decoder as __Decoder,
@@ -317,8 +318,8 @@ export class ACMClient extends __Client<
    */
   readonly config: ACMClientResolvedConfig;
 
-  constructor(configuration: ACMClientConfig) {
-    const _config_0 = __getRuntimeConfig(configuration);
+  constructor(...[configuration]: __CheckOptionalClientConfig<ACMClientConfig>) {
+    const _config_0 = __getRuntimeConfig(configuration || {});
     const _config_1 = resolveClientEndpointParameters(_config_0);
     const _config_2 = resolveRegionConfig(_config_1);
     const _config_3 = resolveEndpointConfig(_config_2);