diff --git a/src/lib/es6.d.ts b/src/lib/es6.d.ts
index 0940f26cac5..5706924e8e3 100644
--- a/src/lib/es6.d.ts
+++ b/src/lib/es6.d.ts
@@ -1,4 +1,4 @@
-declare type PropertyKey = string | number | Symbol;
+declare type PropertyKey = string | number | Symbol;
 
 interface Symbol {
     /** Returns a string representation of an object. */