diff --git a/__tests__/number.spec.js b/__tests__/number.spec.js
index dd4e4bb..9c6bb39 100644
--- a/__tests__/number.spec.js
+++ b/__tests__/number.spec.js
@@ -29,7 +29,21 @@ describe('number', () => {
     });
   });
 
-  it('works for no-required', (done) => {
+  it('works for no-required in case of empty string', (done) => {
+    new Schema({
+      v: {
+        type: 'number',
+        required: false,
+      },
+    }).validate({
+      v: '',
+    }, (errors) => {
+      expect(errors).toBeFalsy();
+      done();
+    });
+  });
+
+  it('works for required', (done) => {
     new Schema({
       v: {
         type: 'number',
diff --git a/src/validator/number.js b/src/validator/number.js
index 7ac41e7..3c20570 100644
--- a/src/validator/number.js
+++ b/src/validator/number.js
@@ -15,6 +15,9 @@ function number(rule, value, callback, source, options) {
   const errors = [];
   const validate = rule.required || (!rule.required && source.hasOwnProperty(rule.field));
   if (validate) {
+    if (value === '') {
+      value = undefined;
+    }
     if (isEmptyValue(value) && !rule.required) {
       return callback();
     }