diff --git a/app/code/Magento/Eav/Model/Entity/Attribute/Backend/JsonEncoded.php b/app/code/Magento/Eav/Model/Entity/Attribute/Backend/JsonEncoded.php
index 5ea8e97e7004f..156c0326f2b6f 100644
--- a/app/code/Magento/Eav/Model/Entity/Attribute/Backend/JsonEncoded.php
+++ b/app/code/Magento/Eav/Model/Entity/Attribute/Backend/JsonEncoded.php
@@ -41,7 +41,7 @@ public function beforeSave($object)
     {
         // parent::beforeSave() is not called intentionally
         $attrCode = $this->getAttribute()->getAttributeCode();
-        if ($object->hasData($attrCode)) {
+        if ($object->hasData($attrCode) && !$this->isJsonEncoded($object->getData($attrCode))) {
             $object->setData($attrCode, $this->jsonSerializer->serialize($object->getData($attrCode)));
         }
         return $this;
@@ -61,4 +61,24 @@ public function afterLoad($object)
         $object->setData($attrCode, $this->jsonSerializer->unserialize($object->getData($attrCode) ?: '{}'));
         return $this;
     }
+
+    /**
+     * Returns true if given value is a valid json value, and false otherwise.
+     *
+     * @param string|int|float|bool|array|null $value
+     * @return bool
+     */
+    private function isJsonEncoded($value): bool
+    {
+        $result = is_string($value);
+        if ($result) {
+            try {
+                $this->jsonSerializer->unserialize($value);
+            } catch (\InvalidArgumentException $e) {
+                $result = false;
+            }
+        }
+
+        return $result;
+    }
 }
diff --git a/app/code/Magento/Eav/Test/Unit/Model/Entity/Attribute/Backend/JsonEncodedTest.php b/app/code/Magento/Eav/Test/Unit/Model/Entity/Attribute/Backend/JsonEncodedTest.php
index d94d25e7fd180..3388cbd3052a8 100644
--- a/app/code/Magento/Eav/Test/Unit/Model/Entity/Attribute/Backend/JsonEncodedTest.php
+++ b/app/code/Magento/Eav/Test/Unit/Model/Entity/Attribute/Backend/JsonEncodedTest.php
@@ -82,6 +82,25 @@ public function testBeforeSave()
         $this->assertEquals(json_encode([1, 2, 3]), $product->getData('json_encoded'));
     }
 
+    /**
+     * Test before save handler with already encoded attribute value
+     */
+    public function testBeforeSaveWithAlreadyEncodedValue()
+    {
+        $product = new \Magento\Framework\DataObject(
+            [
+                'json_encoded' => [1, 2, 3]
+            ]
+        );
+
+        // save twice
+        $this->model->beforeSave($product);
+        $this->model->beforeSave($product);
+        
+        // check it is encoded only once
+        $this->assertEquals(json_encode([1, 2, 3]), $product->getData('json_encoded'));
+    }
+
     /**
      * Test after load handler
      */