diff --git a/src/filesystem/PhutilProcessRef.php b/src/filesystem/PhutilProcessRef.php
index b257067..dabc648 100644
--- a/src/filesystem/PhutilProcessRef.php
+++ b/src/filesystem/PhutilProcessRef.php
@@ -1,80 +1,85 @@
 <?php
 
 final class PhutilProcessRef
   extends Phobject {
 
   private $pid;
   private $command;
   private $isOverseer;
   private $instance;
   private $argv;
 
   public function setPID($pid) {
     $this->pid = $pid;
     return $this;
   }
 
   public function getPID() {
     return $this->pid;
   }
 
   public function getCommand() {
     if (!$this->command) {
       $this->command = phutil_string_cast(csprintf('%LR', $this->argv));
     }
 
     return $this->command;
   }
 
   public function getIsOverseer() {
     if ($this->isOverseer === null) {
       $this->isOverseer = $this->getCommandMatch(
         array(
           array('phd-daemon'),
           array('php', 'phd-daemon'),
         ));
     }
 
     return $this->isOverseer;
   }
 
   public function setInstance($instance) {
     $this->instance = $instance;
     return $this;
   }
 
   public function getInstance() {
     return $this->instance;
   }
 
   private function getCommandMatch(array $patterns) {
     $argv = $this->getArgv();
 
     foreach ($patterns as $pattern) {
       $pattern = array_values($pattern);
       $is_match = true;
       for ($ii = 0; $ii < count($pattern); $ii++) {
+        if (!isset($argv[$ii])) {
+          $is_match = false;
+          break;
+        }
+
         if (basename($argv[$ii]) !== $pattern[$ii]) {
           $is_match = false;
           break;
         }
       }
 
       if ($is_match) {
         return true;
       }
     }
 
     return false;
   }
 
   public function setArgv(array $argv) {
     $this->argv = $argv;
     return $this;
   }
 
   public function getArgv() {
     return $this->argv;
   }
 
 }