diff --git a/src/JsonSerializer/JsonSerializer.php b/src/JsonSerializer/JsonSerializer.php
index ec02718..4b16ea2 100644
--- a/src/JsonSerializer/JsonSerializer.php
+++ b/src/JsonSerializer/JsonSerializer.php
@@ -353,9 +353,41 @@ protected function getObjectProperties($ref, $value)
         foreach ($ref->getProperties() as $prop) {
             $props[] = $prop->getName();
         }
+
+        // Private properties of parent classes are not returned by getProperties() on the child class,
+        // so we traverse the parent chain to collect them.
+        $parentRef = $ref->getParentClass();
+        while ($parentRef !== false) {
+            foreach ($parentRef->getProperties(\ReflectionProperty::IS_PRIVATE) as $prop) {
+                $props[] = $prop->getName();
+            }
+            $parentRef = $parentRef->getParentClass();
+        }
+
         return array_unique(array_merge($props, array_keys(get_object_vars($value))));
     }
 
+    /**
+     * Find a ReflectionProperty by traversing the class hierarchy (needed for parent private properties)
+     *
+     * @param  ReflectionClass $ref
+     * @param  string          $name
+     * @return \ReflectionProperty
+     * @throws ReflectionException
+     */
+    protected function getReflectionProperty($ref, $name)
+    {
+        $classRef = $ref;
+        while ($classRef !== false) {
+            try {
+                return $classRef->getProperty($name);
+            } catch (ReflectionException $e) {
+                $classRef = $classRef->getParentClass();
+            }
+        }
+        throw new ReflectionException('Property ' . $name . ' not found in class ' . $ref->getName() . ' or its parents');
+    }
+
     /**
      * Extract the object data
      *
@@ -369,7 +401,7 @@ protected function extractObjectData($value, $ref, $properties)
         $data = [];
         foreach ($properties as $property) {
             try {
-                $propRef = $ref->getProperty($property);
+                $propRef = $this->getReflectionProperty($ref, $property);
                 $propRef->setAccessible(true);
                 if (!$propRef->isInitialized($value)) {
                     continue;
@@ -515,7 +547,7 @@ protected function unserializeObject($value)
         $this->objectMapping[$this->objectMappingIndex++] = $obj;
         foreach ($value as $property => $propertyValue) {
             try {
-                $propRef = $ref->getProperty($property);
+                $propRef = $this->getReflectionProperty($ref, $property);
                 $propRef->setAccessible(true);
                 $propRef->setValue($obj, $this->unserializeData($propertyValue));
             } catch (ReflectionException $e) {
diff --git a/tests/JsonSerializerTest.php b/tests/JsonSerializerTest.php
index 18b8f3c..f6bdb55 100644
--- a/tests/JsonSerializerTest.php
+++ b/tests/JsonSerializerTest.php
@@ -243,6 +243,29 @@ public function testUnserializeObjects()
     }
 
 
+    /**
+     * Test serialization/unserialization of objects with parent class private properties
+     *
+     * @return void
+     */
+    public function testSerializeObjectWithParentPrivateProperty()
+    {
+        $obj = new SupportClasses\ChildWithParentPrivate();
+        $serialized = $this->serializer->serialize($obj);
+        $this->assertStringContainsString('"parentPrivate":"parentPrivateValue"', $serialized);
+        $this->assertStringContainsString('"childPublic":"childPublicValue"', $serialized);
+        $this->assertStringContainsString('"childPrivate":"childPrivateValue"', $serialized);
+        $this->assertStringContainsString('"parentPublic":"parentPublicValue"', $serialized);
+
+        /** @var SupportClasses\ChildWithParentPrivate $restored */
+        $restored = $this->serializer->unserialize($serialized);
+        $this->assertInstanceOf(SupportClasses\ChildWithParentPrivate::class, $restored);
+        $this->assertSame('parentPrivateValue', $restored->getParentPrivate());
+        $this->assertSame('childPublicValue', $restored->childPublic);
+        $this->assertSame('parentPublicValue', $restored->parentPublic);
+    }
+
+
     /**
      * Test serialization of Enums
      *
diff --git a/tests/SupportClasses/ChildWithParentPrivate.php b/tests/SupportClasses/ChildWithParentPrivate.php
new file mode 100644
index 0000000..a053982
--- /dev/null
+++ b/tests/SupportClasses/ChildWithParentPrivate.php
@@ -0,0 +1,27 @@
+<?php
+
+namespace Zumba\JsonSerializer\Test\SupportClasses;
+
+class ParentWithPrivate
+{
+    private $parentPrivate = 'parentPrivateValue';
+
+    public $parentPublic = 'parentPublicValue';
+
+    public function getParentPrivate()
+    {
+        return $this->parentPrivate;
+    }
+
+    public function setParentPrivate($value)
+    {
+        $this->parentPrivate = $value;
+    }
+}
+
+class ChildWithParentPrivate extends ParentWithPrivate
+{
+    public $childPublic = 'childPublicValue';
+
+    private $childPrivate = 'childPrivateValue';
+}