diff --git a/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php b/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php
index cde5f4a4ee..1ec2c124f5 100644
--- a/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php
+++ b/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php
@@ -1,100 +1,106 @@
 <?php
 
 final class DrydockSSHCommandInterface extends DrydockCommandInterface {
 
   private $passphraseSSHKey;
   private $connectTimeout;
 
   private function openCredentialsIfNotOpen() {
     if ($this->passphraseSSHKey !== null) {
       return;
     }
 
     $credential = id(new PassphraseCredentialQuery())
       ->setViewer(PhabricatorUser::getOmnipotentUser())
       ->withIDs(array($this->getConfig('credential')))
       ->needSecrets(true)
       ->executeOne();
 
+    if ($credential === null) {
+      throw new Exception(pht(
+        'There is no credential with ID %d.',
+        $this->getConfig('credential')));
+    }
+
     if ($credential->getProvidesType() !==
       PassphraseCredentialTypeSSHPrivateKey::PROVIDES_TYPE) {
       throw new Exception('Only private key credentials are supported.');
     }
 
     $this->passphraseSSHKey = PassphraseSSHKey::loadFromPHID(
       $credential->getPHID(),
       PhabricatorUser::getOmnipotentUser());
   }
 
   public function setConnectTimeout($timeout) {
     $this->connectTimeout = $timeout;
     return $this;
   }
 
   public function getExecFuture($command) {
     $this->openCredentialsIfNotOpen();
 
     $argv = func_get_args();
 
     if ($this->getConfig('platform') === 'windows') {
       // Handle Windows by executing the command under PowerShell.
       $command = id(new PhutilCommandString($argv))
         ->setEscapingMode(PhutilCommandString::MODE_POWERSHELL);
 
       $change_directory = '';
       if ($this->getWorkingDirectory() !== null) {
         $change_directory .= 'cd '.$this->getWorkingDirectory();
       }
 
       $script = <<<EOF
 $change_directory
 $command
 if (\$LastExitCode -ne 0) {
   exit \$LastExitCode
 }
 EOF;
 
       // When Microsoft says "Unicode" they don't mean UTF-8.
       $script = mb_convert_encoding($script, 'UTF-16LE');
 
       $script = base64_encode($script);
 
       $powershell =
         'C:\\Windows\\System32\\WindowsPowerShell\\v1.0\\powershell.exe';
       $powershell .=
         ' -ExecutionPolicy Bypass'.
         ' -NonInteractive'.
         ' -InputFormat Text'.
         ' -OutputFormat Text'.
         ' -EncodedCommand '.$script;
 
       $full_command = $powershell;
     } else {
       // Handle UNIX by executing under the native shell.
       $argv = $this->applyWorkingDirectoryToArgv($argv);
 
       $full_command = call_user_func_array('csprintf', $argv);
     }
 
     $command_timeout = '';
     if ($this->connectTimeout !== null) {
       $command_timeout = csprintf(
         '-o %s',
         'ConnectTimeout='.$this->connectTimeout);
     }
 
     return new ExecFuture(
       'ssh '.
       '-o LogLevel=quiet '.
       '-o StrictHostKeyChecking=no '.
       '-o UserKnownHostsFile=/dev/null '.
       '-o BatchMode=yes '.
       '%C -p %s -i %P %P@%s -- %s',
       $command_timeout,
       $this->getConfig('port'),
       $this->passphraseSSHKey->getKeyfileEnvelope(),
       $this->passphraseSSHKey->getUsernameEnvelope(),
       $this->getConfig('host'),
       $full_command);
   }
 }