diff --git a/src/lint/linter/xhpast/rules/ArcanistUnsafeDynamicStringXHPASTLinterRule.php b/src/lint/linter/xhpast/rules/ArcanistUnsafeDynamicStringXHPASTLinterRule.php
index 2cd343bf..bf3c8e51 100644
--- a/src/lint/linter/xhpast/rules/ArcanistUnsafeDynamicStringXHPASTLinterRule.php
+++ b/src/lint/linter/xhpast/rules/ArcanistUnsafeDynamicStringXHPASTLinterRule.php
@@ -1,103 +1,105 @@
 <?php
 
 final class ArcanistUnsafeDynamicStringXHPASTLinterRule
   extends ArcanistXHPASTLinterRule {
 
   const ID = 86;
 
   private $dynamicStringFunctions = array();
   private $dynamicStringClasses   = array();
 
   public function getLintName() {
     return pht('Unsafe Usage of Dynamic String');
   }
 
   public function getLintSeverity() {
     return ArcanistLintSeverity::SEVERITY_ERROR;
   }
 
   public function getLinterConfigurationOptions() {
     $options = array(
       'xhpast.dynamic-string.classes' => array(
         'type' => 'optional map<string, string>',
         'help' => pht(
           'Classes which should should not be used because they represent the '.
           'unsafe usage of dynamic strings.'),
       ),
       'xhpast.dynamic-string.functions' => array(
         'type' => 'optional map<string, string>',
         'help' => pht(
           'Functions which should should not be used because they represent '.
           'the unsafe usage of dynamic strings.'),
       ),
     );
 
     return $options + parent::getLinterConfigurationOptions();
   }
 
   public function setLinterConfigurationValue($key, $value) {
     switch ($key) {
       case 'xhpast.dynamic-string.classes':
         $this->dynamicStringClasses = $value;
         return;
 
       case 'xhpast.dynamic-string.functions':
         $this->dynamicStringFunctions = $value;
         return;
 
       default:
         parent::setLinterConfigurationValue($key, $value);
         return;
     }
   }
 
   public function process(XHPASTNode $root) {
     $this->lintUnsafeDynamicStringClasses($root);
     $this->lintUnsafeDynamicStringFunctions($root);
   }
 
   private function lintUnsafeDynamicStringClasses(XHPASTNode $root) {
     $news = $root->selectDescendantsOfType('n_NEW');
     $this->lintUnsafeDynamicStringCall($news, $this->dynamicStringClasses);
   }
 
   private function lintUnsafeDynamicStringFunctions(XHPASTNode $root) {
     $calls = $root->selectDescendantsOfType('n_FUNCTION_CALL');
     $this->lintUnsafeDynamicStringCall($calls, $this->dynamicStringFunctions);
   }
 
   private function lintUnsafeDynamicStringCall(
     AASTNodeList $calls,
     array $safe) {
 
-    $safe = array_combine(
-      array_map('strtolower', array_keys($safe)),
-      $safe);
+    if ($safe) {
+      $safe = array_combine(
+        array_map('strtolower', array_keys($safe)),
+        $safe);
+    }
 
     foreach ($calls as $call) {
       $name = $call->getChildByIndex(0)->getConcreteString();
       $param = idx($safe, strtolower($name));
 
       if ($param === null) {
         continue;
       }
 
       $parameters = $call->getChildByIndex(1);
       if (count($parameters->getChildren()) <= $param) {
         continue;
       }
 
       $identifier = $parameters->getChildByIndex($param);
       if (!$identifier->isConstantString()) {
         $this->raiseLintAtNode(
           $call,
           pht(
             "Parameter %d of `%s` should be a scalar string, ".
             "otherwise it's not safe.",
             $param + 1,
             $name));
       }
     }
   }
 
 }