diff --git a/src/Optimizely/OptimizelyUserContext.php b/src/Optimizely/OptimizelyUserContext.php
index 1e200038..8769d6f7 100644
--- a/src/Optimizely/OptimizelyUserContext.php
+++ b/src/Optimizely/OptimizelyUserContext.php
@@ -147,6 +147,7 @@ public function getOptimizely()
         return $this->optimizelyClient;
     }
 
+    #[\ReturnTypeWillChange]
     public function jsonSerialize()
     {
         return [