diff --git a/src/DisallowedClassesSubstitutor.php b/src/DisallowedClassesSubstitutor.php
index 9740d1a..eeac7cb 100644
--- a/src/DisallowedClassesSubstitutor.php
+++ b/src/DisallowedClassesSubstitutor.php
@@ -10,7 +10,7 @@
 final class DisallowedClassesSubstitutor
 {
     const PATTERN_STRING = '#s:(\d+):(")#';
-    const PATTERN_OBJECT = '#(^|;)O:\d+:"([^"]*)":(\d+):\{#';
+    const PATTERN_OBJECT = '#(^|;)O:[+-]?\d+:"([^"]*)":(\d+):\{#';
 
     /**
      * @var string