diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index fd1df17b507..625ee963717 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -21059,7 +21059,7 @@ namespace ts {
         function checkExternalEmitHelpers(location: Node, helpers: ExternalEmitHelpers) {
             if ((requestedExternalEmitHelpers & helpers) !== helpers && compilerOptions.importHelpers) {
                 const sourceFile = getSourceFileOfNode(location);
-                if (isEffectiveExternalModule(sourceFile, compilerOptions)) {
+                if (!isDeclarationFile(sourceFile) && isEffectiveExternalModule(sourceFile, compilerOptions)) {
                     const helpersModule = resolveHelpersModule(sourceFile, location);
                     if (helpersModule !== unknownSymbol) {
                         const uncheckedHelpers = helpers & ~requestedExternalEmitHelpers;
@@ -21089,10 +21089,12 @@ namespace ts {
                 case ExternalEmitHelpers.Awaiter: return "__awaiter";
                 case ExternalEmitHelpers.Generator: return "__generator";
                 case ExternalEmitHelpers.Values: return "__values";
-                case ExternalEmitHelpers.Step: return "__step";
-                case ExternalEmitHelpers.Close: return "__close";
                 case ExternalEmitHelpers.Read: return "__read";
                 case ExternalEmitHelpers.Spread: return "__spread";
+                case ExternalEmitHelpers.AsyncGenerator: return "__asyncGenerator";
+                case ExternalEmitHelpers.AsyncDelegator: return "__asyncDelegator";
+                case ExternalEmitHelpers.AsyncValues: return "__asyncValues";
+                default: Debug.fail("Unrecognized helper.");
             }
         }
 
diff --git a/src/compiler/transformers/esnext.ts b/src/compiler/transformers/esnext.ts
index 5685b7ba3c3..5ae49496952 100644
--- a/src/compiler/transformers/esnext.ts
+++ b/src/compiler/transformers/esnext.ts
@@ -858,7 +858,8 @@ namespace ts {
                 function fulfill(value) { resume("next", value); }
                 function reject(value) { resume("throw", value); }
                 function settle(f, v) { c = void 0, f(v), next(); }
-            };`
+            };
+        `
     };
 
     function createAsyncGeneratorHelper(context: TransformationContext, generatorFunc: FunctionExpression) {
@@ -878,28 +879,6 @@ namespace ts {
         );
     }
 
-    const asyncValues: EmitHelper = {
-        name: "typescript:asyncValues",
-        scoped: false,
-        text: `
-            var __asyncValues = (this && this.__asyncIterator) || function (o) {
-                var m = o[Symbol.asyncIterator];
-                if (m) return m.call(o);
-                return typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
-            };
-        `
-    };
-
-    function createAsyncValuesHelper(context: TransformationContext, expression: Expression, location?: TextRange) {
-        context.requestEmitHelper(asyncValues);
-        return createCall(
-            getHelperName("__asyncValues"),
-            /*typeArguments*/ undefined,
-            [expression],
-            location
-        );
-    }
-
     const asyncDelegator: EmitHelper = {
         name: "typescript:asyncDelegator",
         scoped: false,
@@ -921,4 +900,25 @@ namespace ts {
             location
         );
     }
+
+    const asyncValues: EmitHelper = {
+        name: "typescript:asyncValues",
+        scoped: false,
+        text: `
+            var __asyncValues = (this && this.__asyncIterator) || function (o) {
+                var m = o[Symbol.asyncIterator];
+                return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+            };
+        `
+    };
+
+    function createAsyncValuesHelper(context: TransformationContext, expression: Expression, location?: TextRange) {
+        context.requestEmitHelper(asyncValues);
+        return createCall(
+            getHelperName("__asyncValues"),
+            /*typeArguments*/ undefined,
+            [expression],
+            location
+        );
+    }
 }
diff --git a/src/compiler/types.ts b/src/compiler/types.ts
index e44082b2b30..6923e119894 100644
--- a/src/compiler/types.ts
+++ b/src/compiler/types.ts
@@ -3744,20 +3744,17 @@ namespace ts {
         Awaiter = 1 << 6,           // __awaiter (used by ES2017 async functions transformation)
         Generator = 1 << 7,         // __generator (used by ES2015 generator transformation)
         Values = 1 << 8,            // __values (used by ES2015 for..of and yield* transformations)
-        Step = 1 << 9,              // __step (used by ES2015 for..of transformation)
-        Close = 1 << 10,            // __close (used by ES2015 for..of transformation)
-        Read = 1 << 11,             // __read (used by ES2015 iterator destructuring transformation)
-        Spread = 1 << 12,           // __spread (used by ES2015 array spread and argument list spread transformations)
-        AsyncGenerator = 1 << 13,   // __asyncGenerator (used by ES2017 async generator transformation)
-        AsyncValues = 1 << 14,      // __asyncValues (used by ES2017 for..await..of transformation)
-        AsyncStep = 1 << 15,        // __asyncStep (used by ES2017 for..await..of transformation)
-        AsyncDelegator = 1 << 16,   // __asyncDelegator (used by ES2017 async generator yield* transformation)
+        Read = 1 << 9,             // __read (used by ES2015 iterator destructuring transformation)
+        Spread = 1 << 10,           // __spread (used by ES2015 array spread and argument list spread transformations)
+        AsyncGenerator = 1 << 11,   // __asyncGenerator (used by ES2017 async generator transformation)
+        AsyncDelegator = 1 << 12,   // __asyncDelegator (used by ES2017 async generator yield* transformation)
+        AsyncValues = 1 << 13,      // __asyncValues (used by ES2017 for..await..of transformation)
 
         // Helpers included by ES2015 for..of
-        ForOfIncludes = Values | Step | Close,
+        ForOfIncludes = Values,
 
         // Helpers included by ES2017 for..await..of
-        ForAwaitOfIncludes = AsyncValues | AsyncStep | Close,
+        ForAwaitOfIncludes = AsyncValues,
 
         // Helpers included by ES2015 spread
         SpreadIncludes = Read | Spread,
diff --git a/tests/baselines/reference/emitter.forAwait.es2015.js b/tests/baselines/reference/emitter.forAwait.es2015.js
index 5fa516326e1..bfd44581b82 100644
--- a/tests/baselines/reference/emitter.forAwait.es2015.js
+++ b/tests/baselines/reference/emitter.forAwait.es2015.js
@@ -36,8 +36,7 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
 };
 var __asyncValues = (this && this.__asyncIterator) || function (o) {
     var m = o[Symbol.asyncIterator];
-    if (m) return m.call(o);
-    return typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
 };
 function f1() {
     return __awaiter(this, void 0, void 0, function* () {
@@ -68,8 +67,7 @@ var __awaiter = (this && this.__awaiter) || function (thisArg, _arguments, P, ge
 };
 var __asyncValues = (this && this.__asyncIterator) || function (o) {
     var m = o[Symbol.asyncIterator];
-    if (m) return m.call(o);
-    return typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
 };
 function f2() {
     return __awaiter(this, void 0, void 0, function* () {
@@ -92,8 +90,7 @@ function f2() {
 //// [file3.js]
 var __asyncValues = (this && this.__asyncIterator) || function (o) {
     var m = o[Symbol.asyncIterator];
-    if (m) return m.call(o);
-    return typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
 };
 var __asyncGenerator = (this && this.__asyncGenerator) || function (thisArg, _arguments, generator) {
     var g = generator.apply(thisArg, _arguments || []), q = [], c, i;
@@ -128,8 +125,7 @@ function f3() {
 //// [file4.js]
 var __asyncValues = (this && this.__asyncIterator) || function (o) {
     var m = o[Symbol.asyncIterator];
-    if (m) return m.call(o);
-    return typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
 };
 var __asyncGenerator = (this && this.__asyncGenerator) || function (thisArg, _arguments, generator) {
     var g = generator.apply(thisArg, _arguments || []), q = [], c, i;
diff --git a/tests/baselines/reference/emitter.forAwait.es5.js b/tests/baselines/reference/emitter.forAwait.es5.js
index 6dd81f96c7f..5b904cf10a7 100644
--- a/tests/baselines/reference/emitter.forAwait.es5.js
+++ b/tests/baselines/reference/emitter.forAwait.es5.js
@@ -63,8 +63,7 @@ var __generator = (this && this.__generator) || function (thisArg, body) {
 };
 var __asyncValues = (this && this.__asyncIterator) || function (o) {
     var m = o[Symbol.asyncIterator];
-    if (m) return m.call(o);
-    return typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
 };
 function f1() {
     return __awaiter(this, void 0, void 0, function () {
@@ -146,8 +145,7 @@ var __generator = (this && this.__generator) || function (thisArg, body) {
 };
 var __asyncValues = (this && this.__asyncIterator) || function (o) {
     var m = o[Symbol.asyncIterator];
-    if (m) return m.call(o);
-    return typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
 };
 function f2() {
     return __awaiter(this, void 0, void 0, function () {
@@ -221,8 +219,7 @@ var __generator = (this && this.__generator) || function (thisArg, body) {
 };
 var __asyncValues = (this && this.__asyncIterator) || function (o) {
     var m = o[Symbol.asyncIterator];
-    if (m) return m.call(o);
-    return typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
 };
 var __asyncGenerator = (this && this.__asyncGenerator) || function (thisArg, _arguments, generator) {
     var g = generator.apply(thisArg, _arguments || []), q = [], c, i;
@@ -308,8 +305,7 @@ var __generator = (this && this.__generator) || function (thisArg, body) {
 };
 var __asyncValues = (this && this.__asyncIterator) || function (o) {
     var m = o[Symbol.asyncIterator];
-    if (m) return m.call(o);
-    return typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
+    return m ? m.call(o) : typeof __values === "function" ? __values(o) : o[Symbol.iterator]();
 };
 var __asyncGenerator = (this && this.__asyncGenerator) || function (thisArg, _arguments, generator) {
     var g = generator.apply(thisArg, _arguments || []), q = [], c, i;