diff --git a/framework/CHANGELOG.md b/framework/CHANGELOG.md
index 1ba15d3..fa9db15 100644
--- a/framework/CHANGELOG.md
+++ b/framework/CHANGELOG.md
@@ -47,6 +47,7 @@ Yii Framework 2 Change Log
 - Bug #15440: Fixed `yii\behaviors\AttributeTypecastBehavior::$attributeTypes` auto-detection fails for rule, which specify attribute with '!' prefix (klimov-paul)
 - Bug #15462: Fixed `accessChecker` configuration error (developeruz)
 - Bug #15494: Fixed missing `WWW-Authenticate` header (developeruz)
+- Bug #15553: Fixed `yii\validators\NumberValidator` incorrectly validate resource (developeruz)
 - Enh #3087: Added `yii\helpers\BaseHtml::error()` "errorSource" option to be able to customize errors display (yanggs07, developeruz, silverfire)
 - Enh #3250: Added support for events partial wildcard matching (klimov-paul)
 - Enh #5515: Added default value for `yii\behaviors\BlameableBehavior` for cases when the user is guest (dmirogin)
diff --git a/framework/validators/NumberValidator.php b/framework/validators/NumberValidator.php
index 9bf9cde..88b0d41 100644
--- a/framework/validators/NumberValidator.php
+++ b/framework/validators/NumberValidator.php
@@ -81,7 +81,7 @@ class NumberValidator extends Validator
     public function validateAttribute($model, $attribute)
     {
         $value = $model->$attribute;
-        if (is_array($value) || (is_object($value) && !method_exists($value, '__toString'))) {
+        if ($this->isNotNumber($value)) {
             $this->addError($model, $attribute, $this->message);
             return;
         }
@@ -103,7 +103,7 @@ class NumberValidator extends Validator
      */
     protected function validateValue($value)
     {
-        if (is_array($value) || is_object($value)) {
+        if ($this->isNotNumber($value)) {
             return [Yii::t('yii', '{attribute} is invalid.'), []];
         }
         $pattern = $this->integerOnly ? $this->integerPattern : $this->numberPattern;
@@ -118,6 +118,16 @@ class NumberValidator extends Validator
         return null;
     }
 
+    /*
+     * @param mixed $value the data value to be checked.
+     */
+    private function isNotNumber($value)
+    {
+        return is_array($value)
+        || (is_object($value) && !method_exists($value, '__toString'))
+        || (!is_object($value) && !is_scalar($value) && !is_null($value));
+    }
+
     /**
      * {@inheritdoc}
      */
diff --git a/tests/framework/validators/NumberValidatorTest.php b/tests/framework/validators/NumberValidatorTest.php
index e794eeb..fa3edfa 100644
--- a/tests/framework/validators/NumberValidatorTest.php
+++ b/tests/framework/validators/NumberValidatorTest.php
@@ -298,4 +298,45 @@ class NumberValidatorTest extends TestCase
         $value = new \stdClass();
         $this->assertFalse($val->validate($value));
     }
+
+    public function testValidateResource()
+    {
+        $val = new NumberValidator();
+        $fp = fopen('php://stdin', 'r');
+        $this->assertFalse($val->validate($fp));
+
+        $model = new FakedValidationModel();
+        $model->attr_number = $fp;
+        $val->validateAttribute($model, 'attr_number');
+        $this->assertTrue($model->hasErrors('attr_number'));
+
+        fclose($fp);
+    }
+
+    public function testValidateToString()
+    {
+        $val = new NumberValidator();
+        $object = new TestClass('10');
+        $this->assertTrue($val->validate($object));
+
+        $model = new FakedValidationModel();
+        $model->attr_number = $object;
+        $val->validateAttribute($model, 'attr_number');
+        $this->assertFalse($model->hasErrors('attr_number'));
+    }
+}
+
+class TestClass
+{
+    public $foo;
+
+    public function __construct($foo)
+    {
+        $this->foo = $foo;
+    }
+
+    public function __toString()
+    {
+        return $this->foo;
+    }
 }