diff --git a/src/lib/es2015.core.d.ts b/src/lib/es2015.core.d.ts
index 819d89eb0c4..71a8655350f 100644
--- a/src/lib/es2015.core.d.ts
+++ b/src/lib/es2015.core.d.ts
@@ -402,6 +402,14 @@ interface String {
       */
     endsWith(searchString: string, endPosition?: number): boolean;
 
+    /**
+      * Returns the String value result of normalizing the string into the normalization form
+      * named by form as specified in Unicode Standard Annex #15, Unicode Normalization Forms.
+      * @param form Applicable values: "NFC", "NFD", "NFKC", or "NFKD", If not specified default
+      * is "NFC"
+      */
+    normalize(form: "NFC" | "NFD" | "NFKC" | "NFKD"): string;
+
     /**
       * Returns the String value result of normalizing the string into the normalization form
       * named by form as specified in Unicode Standard Annex #15, Unicode Normalization Forms.