diff --git a/src/Handler.php b/src/Handler.php
index 236aaee..0e85429 100644
--- a/src/Handler.php
+++ b/src/Handler.php
@@ -203,7 +203,9 @@ public function handleError(int $level, string $message, string $file, int $line
         if ($event !== null) {
             $this->send($event);
 
-            return false !== ($this->previousErrorHandler)($level, $message, $file, $line);
+            if (null !== $this->previousErrorHandler) {
+                return false !== ($this->previousErrorHandler)($level, $message, $file, $line);
+            }
         }
 
         return false;