diff --git a/package-lock.json b/package-lock.json
index 476ef56..c75c506 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,6 +1,6 @@
 {
   "name": "not-me",
-  "version": "4.3.3",
+  "version": "4.3.5",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {
diff --git a/package.json b/package.json
index 1b46c54..33914a9 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "not-me",
-  "version": "4.3.4",
+  "version": "4.3.5",
   "description": "Easy and type-safe validation",
   "main": "lib/index.js",
   "types": "lib/types.d.ts",
diff --git a/src/schemas/number/number-schema.spec.ts b/src/schemas/number/number-schema.spec.ts
index feb5839..fab8c07 100644
--- a/src/schemas/number/number-schema.spec.ts
+++ b/src/schemas/number/number-schema.spec.ts
@@ -19,4 +19,13 @@ describe("Number Schema", () => {
       value: 123.3,
     });
   });
+
+  it("Let undefined pass an integer check, if number is not required", () => {
+    const schema: Schema<number | undefined | null> = number().integer();
+
+    expect(schema.validate(undefined)).toEqual({
+      errors: false,
+      value: undefined,
+    });
+  });
 });
diff --git a/src/schemas/number/number-schema.ts b/src/schemas/number/number-schema.ts
index 5562f1b..a4565e9 100644
--- a/src/schemas/number/number-schema.ts
+++ b/src/schemas/number/number-schema.ts
@@ -38,14 +38,18 @@ class NumberSchemaImpl<_Output = number | undefined | null> extends BaseSchema<
   }
 
   integer(message?: string): this {
-    this.test((input) =>
-      Number.isInteger(input)
-        ? null
-        : message ||
-          DefaultErrorMessagesManager.getDefaultMessages().number
-            ?.isNotInteger ||
-          "Input must be an integer"
-    );
+    this.test((input) => {
+      if (input == null) {
+        return null;
+      } else {
+        return Number.isInteger(input)
+          ? null
+          : message ||
+              DefaultErrorMessagesManager.getDefaultMessages().number
+                ?.isNotInteger ||
+              "Input must be an integer";
+      }
+    });
 
     return this;
   }