diff --git a/src/PHPCensor/Plugin/PhpParallelLint.php b/src/PHPCensor/Plugin/PhpParallelLint.php
index f3a6daeb..5fa044bb 100644
--- a/src/PHPCensor/Plugin/PhpParallelLint.php
+++ b/src/PHPCensor/Plugin/PhpParallelLint.php
@@ -59,7 +59,11 @@ class PhpParallelLint extends Plugin
         }
 
         if (isset($options['extensions'])) {
-            $this->extensions = $options['extensions'];
+            // Only use if this is a comma delimited list
+            $pattern = '/^[a-z]*,\\ *[a-z]*$/';
+            if (preg_match($pattern, $options['extensions'])) {
+                $this->extensions = $options['extensions'];
+            }
         }
     }