diff --git a/src/util/config.spec.ts b/src/util/config.spec.ts
index 55351b6b..60ce2323 100644
--- a/src/util/config.spec.ts
+++ b/src/util/config.spec.ts
@@ -162,7 +162,7 @@ describe('config', () => {
       expect(fakeConfig[Constants.ENV_EXPERIMENTAL_MANUAL_TREESHAKING]).toBeFalsy();
       expect(fakeConfig[Constants.ENV_USE_EXPERIMENTAL_CLOSURE]).toBeFalsy();
       expect(fakeConfig[Constants.ENV_USE_EXPERIMENTAL_BABILI]).toBeFalsy();
-      expect(fakeConfig[Constants.ENV_BUILD_TO_ES5]).toBeFalsy();
+      expect(fakeConfig[Constants.ENV_BUILD_TO_ES5]).toEqual('true');
       expect(context.bundler).toEqual('webpack');
     });
 
diff --git a/src/util/config.ts b/src/util/config.ts
index 064598a3..34c8d9c1 100644
--- a/src/util/config.ts
+++ b/src/util/config.ts
@@ -304,7 +304,7 @@ export function generateContext(context?: BuildContext): BuildContext {
 
   // default stand-alone builds to default to es5
   // if closure is being used, don't worry about this as it already automatically converts to ES5
-  const buildToEs5 = getConfigValue(context, '--buildToEs5', null, Constants.ENV_BUILD_TO_ES5, Constants.ENV_BUILD_TO_ES5.toLowerCase(), null);
+  const buildToEs5 = getConfigValue(context, '--buildToEs5', null, Constants.ENV_BUILD_TO_ES5, Constants.ENV_BUILD_TO_ES5.toLowerCase(), useExperimentalClosure ? null : 'true');
   setProcessEnvVar(Constants.ENV_BUILD_TO_ES5, buildToEs5);
   Logger.debug(`buildToEs5 set to ${buildToEs5}`);