diff --git a/src/compiler/checker.ts b/src/compiler/checker.ts
index 0567712f11da3..82ec2c275f711 100644
--- a/src/compiler/checker.ts
+++ b/src/compiler/checker.ts
@@ -13785,13 +13785,14 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
             && isTypeUsableAsIndexSignature(isComputedPropertyName(node) ? checkComputedPropertyName(node) : checkExpressionCached((node as ElementAccessExpression).argumentExpression));
     }
 
-    function isLateBindableAST(node: DeclarationName) {
-        if (!isComputedPropertyName(node) && !isElementAccessExpression(node)) {
-            return false;
-        }
-        const expr = isComputedPropertyName(node) ? node.expression : node.argumentExpression;
-        return isEntityNameExpression(expr);
-    }
+    function isLateBindableAST(node: DeclarationName) {
+        if (!isComputedPropertyName(node) && !isElementAccessExpression(node)) {
+            return false;
+        }
+        const expr = isComputedPropertyName(node) ? node.expression : node.argumentExpression;
+        return isEntityNameExpression(expr) ||
+            isElementAccessExpression(expr) && isStringLiteral(expr.argumentExpression) && isEntityNameExpression(expr.expression);
+    }
 
     function isTypeUsableAsIndexSignature(type: Type): boolean {
         return isTypeAssignableTo(type, stringNumberSymbolType);
diff --git a/src/lib/es2015.collection.d.ts b/src/lib/es2015.collection.d.ts
index 43129531845e4..a01b21dded868 100644
--- a/src/lib/es2015.collection.d.ts
+++ b/src/lib/es2015.collection.d.ts
@@ -94,7 +94,7 @@ interface Set<T> {
      */
     has(value: T): boolean;
     /**
-     * @returns the number of (unique) elements in Set.
+     * @returns the number of (unique) elements in the Set.
      */
     readonly size: number;
 }