diff --git a/snippets/isNumber.md b/snippets/isNumber.md
index 8e02406af..a692c8f9a 100644
--- a/snippets/isNumber.md
+++ b/snippets/isNumber.md
@@ -2,13 +2,14 @@
 
 Checks if the given argument is a number.
 
-Use `typeof` to check if a value is classified as a number primitive.
+Use `typeof` to check if a value is classified as a number primitive. Because `typeof NaN` is equal to `number`, the `val === val` is for protection. NaN compares unequal (via ==, !=, ===, and !==) to any other value, including to another NaN value.
 
 ```js
-const isNumber = val => typeof val === 'number';
+const isNumber = val => typeof val === 'number' && val === val;
 ```
 
 ```js
-isNumber('1'); // false
 isNumber(1); // true
+isNumber('1'); // false
+isNumber(NaN); // false
 ```
diff --git a/test/isNumber.test.js b/test/isNumber.test.js
index 4f27fe9ca..90ca4ec6c 100644
--- a/test/isNumber.test.js
+++ b/test/isNumber.test.js
@@ -10,3 +10,6 @@ test('passed argument is a number', () => {
 test('passed argument is not a number', () => {
   expect(isNumber('1')).toBeFalsy();
 });
+test('passed argument is not a number', () => {
+  expect(isNumber(NaN)).toBeFalsy();
+});