diff --git a/src/Monolog/Formatter/JsonFormatter.php b/src/Monolog/Formatter/JsonFormatter.php
index b737d82e3..753e6852c 100644
--- a/src/Monolog/Formatter/JsonFormatter.php
+++ b/src/Monolog/Formatter/JsonFormatter.php
@@ -192,6 +192,10 @@ protected function normalize($data, int $depth = 0)
                 return $data;
             }
 
+            if (\get_class($data) === '__PHP_Incomplete_Class') {
+                return new \ArrayObject($data);
+            }
+
             if (method_exists($data, '__toString')) {
                 return $data->__toString();
             }
diff --git a/tests/Monolog/Formatter/JsonFormatterTest.php b/tests/Monolog/Formatter/JsonFormatterTest.php
index 147021029..33f6b4d7d 100644
--- a/tests/Monolog/Formatter/JsonFormatterTest.php
+++ b/tests/Monolog/Formatter/JsonFormatterTest.php
@@ -297,6 +297,18 @@ public function testNormalizeHandleLargeArrays()
         $this->assertEquals('Over 1000 items (2000 total), aborting normalization', $res['context'][0]['...']);
     }
 
+    public function testCanNormalizeIncompleteObject(): void
+    {
+        $serialized = "O:17:\"Monolog\TestClass\":1:{s:23:\"\x00Monolog\TestClass\x00name\";s:4:\"test\";}";
+        $object = unserialize($serialized);
+
+        $formatter = new JsonFormatter();
+        $record = ['context' => ['object' => $object]];
+        $result = $formatter->format($record);
+
+        self::assertSame('{"context":{"object":{"__PHP_Incomplete_Class_Name":"Monolog\\\\TestClass"}}}'."\n", $result);
+    }
+
     public function testEmptyContextAndExtraFieldsCanBeIgnored()
     {
         $formatter = new JsonFormatter(JsonFormatter::BATCH_MODE_JSON, true, true);