diff --git a/src/main/php/PHP/PMD/Rule/UnusedPrivateField.php b/src/main/php/PHP/PMD/Rule/UnusedPrivateField.php
index 0d492c74c..7d542abfc 100644
--- a/src/main/php/PHP/PMD/Rule/UnusedPrivateField.php
+++ b/src/main/php/PHP/PMD/Rule/UnusedPrivateField.php
@@ -202,6 +202,9 @@ protected function isValidPropertyNode(PHP_PMD_Node_ASTNode $node = null)
                 return false;
             }
             $parent = $parent->getParent();
+            if (is_null($parent)) {
+                   return false;
+            }
         }
         return true;
     }