diff --git a/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php b/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php
--- a/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php
+++ b/src/applications/drydock/interface/command/DrydockSSHCommandInterface.php
@@ -36,18 +36,44 @@
 
     $argv = func_get_args();
 
-    // This assumes there's a UNIX shell living at the other
-    // end of the connection, which isn't the case for Windows machines.
-    if ($this->getConfig('platform') !== 'windows') {
-      $argv = $this->applyWorkingDirectoryToArgv($argv);
-    }
+    if ($this->getConfig('platform') === 'windows') {
+      // Handle Windows by executing the command under PowerShell.
+      $command = id(new PhutilCommandString($argv))
+        ->setEscapingMode(PhutilCommandString::MODE_POWERSHELL);
 
-    $full_command = call_user_func_array('csprintf', $argv);
+      $change_directory = '';
+      if ($this->getWorkingDirectory() !== null) {
+        $change_directory .= 'cd '.$this->getWorkingDirectory();
+      }
 
-    if ($this->getConfig('platform') === 'windows') {
-      // On Windows platforms we need to execute cmd.exe explicitly since
-      // most commands are not really executables.
-      $full_command = 'C:\\Windows\\system32\\cmd.exe /C '.$full_command;
+      $script = <<<EOF
+$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 = '';
diff --git a/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php b/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php
--- a/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php
+++ b/src/applications/harbormaster/step/HarbormasterCommandBuildStepImplementation.php
@@ -3,6 +3,8 @@
 final class HarbormasterCommandBuildStepImplementation
   extends HarbormasterBuildStepImplementation {
 
+  private $platform;
+
   public function getName() {
     return pht('Run Command');
   }
@@ -18,6 +20,18 @@
       $this->formatSettingForDescription('hostartifact'));
   }
 
+  public function escapeCommand($pattern, $args) {
+    array_unshift($args, $pattern);
+
+    $mode = PhutilCommandString::MODE_DEFAULT;
+    if ($this->platform == 'windows') {
+      $mode = PhutilCommandString::MODE_POWERSHELL;
+    }
+
+    return id(new PhutilCommandString($args))
+      ->setEscapingMode($mode);
+  }
+
   public function execute(
     HarbormasterBuild $build,
     HarbormasterBuildTarget $build_target) {
@@ -25,14 +39,18 @@
     $settings = $this->getSettings();
     $variables = $build_target->getVariables();
 
+    $artifact = $build->loadArtifact($settings['hostartifact']);
+
+    $lease = $artifact->loadDrydockLease();
+
+    $this->platform = $lease->getAttribute('platform');
+
     $command = $this->mergeVariables(
-      'vcsprintf',
+      array($this, 'escapeCommand'),
       $settings['command'],
       $variables);
 
-    $artifact = $build->loadArtifact($settings['hostartifact']);
-
-    $lease = $artifact->loadDrydockLease();
+    $this->platform = null;
 
     $interface = $lease->getInterface('command');
 
@@ -88,6 +106,9 @@
         'name' => pht('Command'),
         'type' => 'text',
         'required' => true,
+        'caption' => pht(
+          'Under Windows, this is executed under PowerShell.'.
+          'Under UNIX, this is executed using the user\'s shell.'),
       ),
       'hostartifact' => array(
         'name' => pht('Host'),