diff --git a/.eslintrc b/.eslintrc
index b59cdc47dca..f873c3c7619 100644
--- a/.eslintrc
+++ b/.eslintrc
@@ -52,7 +52,7 @@
 
         "microsoft-typescript/object-literal-surrounding-space": "error",
         "microsoft-typescript/no-type-assertion-whitespace": "error",
-        "microsoft-typescript/type-operator-spacing": "off",
+        "microsoft-typescript/type-operator-spacing": "error",
         "microsoft-typescript/only-arrow-functions": "off",
         "microsoft-typescript/no-double-space": "off",
         "microsoft-typescript/boolean-trivia": "error",
diff --git a/src/lib/es2019.array.d.ts b/src/lib/es2019.array.d.ts
index 33bee0c205e..07fc76a9c77 100644
--- a/src/lib/es2019.array.d.ts
+++ b/src/lib/es2019.array.d.ts
@@ -11,7 +11,7 @@ interface ReadonlyArray<T> {
      * thisArg is omitted, undefined is used as the this value.
      */
     flatMap<U, This = undefined> (
-        callback: (this: This, value: T, index: number, array: T[]) => U|ReadonlyArray<U>,
+        callback: (this: This, value: T, index: number, array: T[]) => U | ReadonlyArray<U>,
         thisArg?: This
     ): U[]
 
@@ -125,7 +125,7 @@ interface Array<T> {
      * thisArg is omitted, undefined is used as the this value.
      */
     flatMap<U, This = undefined> (
-        callback: (this: This, value: T, index: number, array: T[]) => U|ReadonlyArray<U>,
+        callback: (this: This, value: T, index: number, array: T[]) => U | ReadonlyArray<U>,
         thisArg?: This
     ): U[]