diff --git a/src/lib/es2015.core.d.ts b/src/lib/es2015.core.d.ts
index 356512ecf5..28f2e12248 100644
--- a/src/lib/es2015.core.d.ts
+++ b/src/lib/es2015.core.d.ts
@@ -205,13 +205,13 @@ interface NumberConstructor {
       * number. Only finite values of the type number, result in true.
       * @param number A numeric value.
       */
-    isFinite(number: number): boolean;
+    isFinite(value: any): value is number;
 
     /**
       * Returns true if the value passed is an integer, false otherwise.
       * @param number A numeric value.
       */
-    isInteger(number: number): boolean;
+    isInteger(value: any): value is number;
 
     /**
       * Returns a Boolean value that indicates whether a value is the reserved value NaN (not a
@@ -219,13 +219,13 @@ interface NumberConstructor {
       * to a number. Only values of the type number, that are also NaN, result in true.
       * @param number A numeric value.
       */
-    isNaN(number: number): boolean;
+    isNaN(value: any): value is number;
 
     /**
       * Returns true if the value passed is a safe integer.
       * @param number A numeric value.
       */
-    isSafeInteger(number: number): boolean;
+    isSafeInteger(value: any): value is number;
 
     /**
       * The value of the largest integer n such that n and n + 1 are both exactly representable as