diff --git a/private/my-local-model-schema/src/XYZServiceClient.ts b/private/my-local-model-schema/src/XYZServiceClient.ts
index 0e614dbc8dd..09463e9a9a2 100644
--- a/private/my-local-model-schema/src/XYZServiceClient.ts
+++ b/private/my-local-model-schema/src/XYZServiceClient.ts
@@ -254,7 +254,7 @@ export class XYZServiceClient extends __Client<
     const _config_4 = resolveEndpointRequiredConfig(_config_3);
     const _config_5 = resolveEventStreamSerdeConfig(_config_4);
     const _config_6 = resolveHttpAuthSchemeConfig(_config_5);
-    let _config_7 = resolveRuntimeExtensions(_config_6, configuration?.extensions || []);
+    const _config_7 = resolveRuntimeExtensions(_config_6, configuration?.extensions || []);
     this.config = _config_7;
     this.middlewareStack.use(getSchemaSerdePlugin(this.config));
     this.middlewareStack.use(getRetryPlugin(this.config));
diff --git a/private/my-local-model/src/XYZServiceClient.ts b/private/my-local-model/src/XYZServiceClient.ts
index a861594f22d..81625d9b1a2 100644
--- a/private/my-local-model/src/XYZServiceClient.ts
+++ b/private/my-local-model/src/XYZServiceClient.ts
@@ -240,7 +240,7 @@ export class XYZServiceClient extends __Client<
     const _config_4 = resolveEndpointRequiredConfig(_config_3);
     const _config_5 = resolveEventStreamSerdeConfig(_config_4);
     const _config_6 = resolveHttpAuthSchemeConfig(_config_5);
-    let _config_7 = resolveRuntimeExtensions(_config_6, configuration?.extensions || []);
+    const _config_7 = resolveRuntimeExtensions(_config_6, configuration?.extensions || []);
     this.config = _config_7;
     this.middlewareStack.use(getRetryPlugin(this.config));
     this.middlewareStack.use(getContentLengthPlugin(this.config));
diff --git a/private/smithy-rpcv2-cbor-schema/src/RpcV2ProtocolClient.ts b/private/smithy-rpcv2-cbor-schema/src/RpcV2ProtocolClient.ts
index 34dad028f4b..2e108514c8c 100644
--- a/private/smithy-rpcv2-cbor-schema/src/RpcV2ProtocolClient.ts
+++ b/private/smithy-rpcv2-cbor-schema/src/RpcV2ProtocolClient.ts
@@ -300,7 +300,7 @@ export class RpcV2ProtocolClient extends __Client<
     const _config_3 = resolveEndpointConfig(_config_2);
     const _config_4 = resolveEndpointRequiredConfig(_config_3);
     const _config_5 = resolveHttpAuthSchemeConfig(_config_4);
-    let _config_6 = resolveRuntimeExtensions(_config_5, configuration?.extensions || []);
+    const _config_6 = resolveRuntimeExtensions(_config_5, configuration?.extensions || []);
     this.config = _config_6;
     this.middlewareStack.use(getSchemaSerdePlugin(this.config));
     this.middlewareStack.use(getRetryPlugin(this.config));
diff --git a/private/smithy-rpcv2-cbor/src/RpcV2ProtocolClient.ts b/private/smithy-rpcv2-cbor/src/RpcV2ProtocolClient.ts
index 5bf07aafaa3..296969ed836 100644
--- a/private/smithy-rpcv2-cbor/src/RpcV2ProtocolClient.ts
+++ b/private/smithy-rpcv2-cbor/src/RpcV2ProtocolClient.ts
@@ -277,7 +277,7 @@ export class RpcV2ProtocolClient extends __Client<
     const _config_3 = resolveEndpointConfig(_config_2);
     const _config_4 = resolveEndpointRequiredConfig(_config_3);
     const _config_5 = resolveHttpAuthSchemeConfig(_config_4);
-    let _config_6 = resolveRuntimeExtensions(_config_5, configuration?.extensions || []);
+    const _config_6 = resolveRuntimeExtensions(_config_5, configuration?.extensions || []);
     this.config = _config_6;
     this.middlewareStack.use(getRetryPlugin(this.config));
     this.middlewareStack.use(getContentLengthPlugin(this.config));
diff --git a/smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/ServiceBareBonesClientGenerator.java b/smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/ServiceBareBonesClientGenerator.java
index 10f49c61a0a..5e07f0c3937 100644
--- a/smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/ServiceBareBonesClientGenerator.java
+++ b/smithy-typescript-codegen/src/main/java/software/amazon/smithy/typescript/codegen/ServiceBareBonesClientGenerator.java
@@ -429,7 +429,7 @@ private void generateConstructor() {
                 Paths.get(".", CodegenUtils.SOURCE_FOLDER, "runtimeExtensions"));
 
             configVariable++;
-            writer.write("let $L = resolveRuntimeExtensions($L, configuration?.extensions || []);",
+            writer.write("const $L = resolveRuntimeExtensions($L, configuration?.extensions || []);",
                 generateConfigVariable(configVariable),
                 generateConfigVariable(configVariable - 1));