diff --git a/packages/build/src/optimize-streams.ts b/packages/build/src/optimize-streams.ts
index ed6c0ea98..52d1e8aec 100644
--- a/packages/build/src/optimize-streams.ts
+++ b/packages/build/src/optimize-streams.ts
@@ -105,6 +105,26 @@ export class GenericOptimizeTransform extends Transform {
   }
 }
 
+function getCompileTarget(
+    file: vinyl, options: JsOptimizeOptions): JsCompileTarget|boolean {
+  let target: JsCompileTarget|boolean|undefined;
+  const compileOptions = options.compile;
+  if (notExcluded(options.compile)(file)) {
+    if (typeof compileOptions === 'object') {
+      target =
+          (compileOptions.target === undefined) ? true : compileOptions.target;
+    } else {
+      target = compileOptions;
+    }
+    if (target === undefined) {
+      target = false;
+    }
+  } else {
+    target = false;
+  }
+  return target;
+}
+
 /**
  * Transform JavaScript.
  */
@@ -112,26 +132,6 @@ export class JsTransform extends GenericOptimizeTransform {
   constructor(options: OptimizeOptions) {
     const jsOptions: JsOptimizeOptions = options.js || {};
 
-    function getCompileTarget(file: vinyl): JsCompileTarget|boolean {
-      let target: JsCompileTarget|boolean|undefined;
-      const compileOptions = jsOptions.compile;
-      if (notExcluded(jsOptions.compile)(file)) {
-        if (typeof compileOptions === 'object') {
-          target = (compileOptions.target === undefined) ?
-              true :
-              compileOptions.target;
-        } else {
-          target = compileOptions;
-        }
-        if (target === undefined) {
-          target = false;
-        }
-      } else {
-        target = false;
-      }
-      return target;
-    }
-
     const shouldMinifyFile =
         jsOptions.minify ? notExcluded(jsOptions.minify) : () => false;
 
@@ -153,7 +153,7 @@ export class JsTransform extends GenericOptimizeTransform {
       }
 
       return jsTransform(content, {
-        compile: getCompileTarget(file),
+        compile: getCompileTarget(file, jsOptions),
         externalHelpers: true,
         minify: shouldMinifyFile(file),
         moduleResolution: jsOptions.moduleResolution,
@@ -173,7 +173,7 @@ export class JsTransform extends GenericOptimizeTransform {
  */
 export class HtmlTransform extends GenericOptimizeTransform {
   constructor(options: OptimizeOptions) {
-    const anyJsCompiledToEs5 = options.js && !!options.js.compile;
+    const jsOptions: JsOptimizeOptions = options.js || {};
 
     const shouldMinifyFile = options.html && options.html.minify ?
         notExcluded(options.html.minify) :
@@ -188,11 +188,27 @@ export class HtmlTransform extends GenericOptimizeTransform {
       let injectBabelHelpers: 'none'|'full'|'amd' = 'none';
       let injectRegeneratorRuntime = false;
       if (isEntryPoint) {
-        if (anyJsCompiledToEs5) {
-          injectBabelHelpers = 'full';
-          injectRegeneratorRuntime = true;
-        } else if (transformModulesToAmd) {
-          injectBabelHelpers = 'amd';
+        const compileTarget = getCompileTarget(file, jsOptions);
+        switch (compileTarget) {
+          case 'es5':
+          case true:
+            injectBabelHelpers = 'full';
+            injectRegeneratorRuntime = true;
+            break;
+          case 'es2015':
+          case 'es2016':
+          case 'es2017':
+            injectBabelHelpers = 'full';
+            injectRegeneratorRuntime = false;
+            break;
+          case 'es2018':
+          case false:
+            injectBabelHelpers = transformModulesToAmd ? 'amd' : 'none';
+            injectRegeneratorRuntime = false;
+            break;
+          default:
+            const never: never = compileTarget;
+            throw new Error(`Unexpected compile target ${never}`);
         }
       }