diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -187,7 +187,9 @@
     'ArcanistFileUploader' => 'upload/ArcanistFileUploader.php',
     'ArcanistFilenameLinter' => 'lint/linter/ArcanistFilenameLinter.php',
     'ArcanistFilenameLinterTestCase' => 'lint/linter/__tests__/ArcanistFilenameLinterTestCase.php',
+    'ArcanistFilesystemAPI' => 'repository/api/ArcanistFilesystemAPI.php',
     'ArcanistFilesystemConfigurationSource' => 'config/source/ArcanistFilesystemConfigurationSource.php',
+    'ArcanistFilesystemWorkingCopy' => 'workingcopy/ArcanistFilesystemWorkingCopy.php',
     'ArcanistFlagWorkflow' => 'workflow/ArcanistFlagWorkflow.php',
     'ArcanistFlake8Linter' => 'lint/linter/ArcanistFlake8Linter.php',
     'ArcanistFlake8LinterTestCase' => 'lint/linter/__tests__/ArcanistFlake8LinterTestCase.php',
@@ -1130,7 +1132,9 @@
     'ArcanistFileUploader' => 'Phobject',
     'ArcanistFilenameLinter' => 'ArcanistLinter',
     'ArcanistFilenameLinterTestCase' => 'ArcanistLinterTestCase',
+    'ArcanistFilesystemAPI' => 'ArcanistRepositoryAPI',
     'ArcanistFilesystemConfigurationSource' => 'ArcanistDictionaryConfigurationSource',
+    'ArcanistFilesystemWorkingCopy' => 'ArcanistWorkingCopy',
     'ArcanistFlagWorkflow' => 'ArcanistWorkflow',
     'ArcanistFlake8Linter' => 'ArcanistExternalLinter',
     'ArcanistFlake8LinterTestCase' => 'ArcanistExternalLinterTestCase',
diff --git a/src/repository/api/ArcanistFilesystemAPI.php b/src/repository/api/ArcanistFilesystemAPI.php
new file mode 100644
--- /dev/null
+++ b/src/repository/api/ArcanistFilesystemAPI.php
@@ -0,0 +1,100 @@
+<?php
+
+final class ArcanistFilesystemAPI
+  extends ArcanistRepositoryAPI {
+
+  public function getSourceControlSystemName() {
+    return 'filesystem';
+  }
+
+  protected function buildUncommittedStatus() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  protected function buildCommitRangeStatus() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getAllFiles() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getBlame($path) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getRawDiffText($path) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getOriginalFileData($path) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getCurrentFileData($path) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getLocalCommitInformation() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getSourceControlBaseRevision() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getCanonicalRevisionName($string) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getBranchName() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getSourceControlPath() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function isHistoryDefaultImmutable() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function supportsAmend() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getWorkingCopyRevision() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function updateWorkingCopy() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getMetadataPath() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function loadWorkingCopyDifferentialRevisions(
+    ConduitClient $conduit,
+    array $query) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function getRemoteURI() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function supportsLocalCommits() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  protected function buildLocalFuture(array $argv) {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+  public function supportsCommitRanges() {
+    throw new PhutilMethodNotImplementedException();
+  }
+
+}
diff --git a/src/toolset/workflow/ArcanistVersionWorkflow.php b/src/toolset/workflow/ArcanistVersionWorkflow.php
--- a/src/toolset/workflow/ArcanistVersionWorkflow.php
+++ b/src/toolset/workflow/ArcanistVersionWorkflow.php
@@ -48,15 +48,10 @@
     );
 
     foreach ($roots as $lib => $root) {
-      $is_git = false;
-
       $working_copy = ArcanistWorkingCopy::newFromWorkingDirectory($root);
-      if ($working_copy) {
-        $repository_api = $working_copy->newRepositoryAPI();
-        if ($repository_api instanceof ArcanistGitAPI) {
-          $is_git = true;
-        }
-      }
+
+      $repository_api = $working_copy->getRepositoryAPI();
+      $is_git = ($repository_api instanceof ArcanistGitAPI);
 
       if (!$is_git) {
         throw new PhutilArgumentUsageException(
diff --git a/src/workflow/ArcanistUpgradeWorkflow.php b/src/workflow/ArcanistUpgradeWorkflow.php
--- a/src/workflow/ArcanistUpgradeWorkflow.php
+++ b/src/workflow/ArcanistUpgradeWorkflow.php
@@ -43,15 +43,10 @@
           'Preparing to upgrade "%s"...',
           $library));
 
-      $is_git = false;
-
       $working_copy = ArcanistWorkingCopy::newFromWorkingDirectory($root);
-      if ($working_copy) {
-        $repository_api = $working_copy->newRepositoryAPI();
-        if ($repository_api instanceof ArcanistGitAPI) {
-          $is_git = true;
-        }
-      }
+
+      $repository_api = $working_copy->getRepositoryAPI();
+      $is_git = ($repository_api instanceof ArcanistGitAPI);
 
       if (!$is_git) {
         throw new PhutilArgumentUsageException(
diff --git a/src/workingcopy/ArcanistFilesystemWorkingCopy.php b/src/workingcopy/ArcanistFilesystemWorkingCopy.php
new file mode 100644
--- /dev/null
+++ b/src/workingcopy/ArcanistFilesystemWorkingCopy.php
@@ -0,0 +1,27 @@
+<?php
+
+final class ArcanistFilesystemWorkingCopy
+  extends ArcanistWorkingCopy {
+
+  public function getMetadataDirectory() {
+    return null;
+  }
+
+  protected function newWorkingCopyFromDirectories(
+    $working_directory,
+    $ancestor_directory) {
+    return null;
+  }
+
+  protected function newRepositoryAPI() {
+    return new ArcanistFilesystemAPI();
+  }
+
+  public function getProjectConfigurationFilePath() {
+    // We don't support project-level configuration for "filesytem" working
+    // copies because scattering random ".arcconfig" files around the
+    // filesystem and having them affect program behavior is silly.
+    return null;
+  }
+
+}
diff --git a/src/workingcopy/ArcanistGitWorkingCopy.php b/src/workingcopy/ArcanistGitWorkingCopy.php
--- a/src/workingcopy/ArcanistGitWorkingCopy.php
+++ b/src/workingcopy/ArcanistGitWorkingCopy.php
@@ -18,7 +18,7 @@
     return new self();
   }
 
-  public function newRepositoryAPI() {
+  protected function newRepositoryAPI() {
     return new ArcanistGitAPI($this->getPath());
   }
 
diff --git a/src/workingcopy/ArcanistMercurialWorkingCopy.php b/src/workingcopy/ArcanistMercurialWorkingCopy.php
--- a/src/workingcopy/ArcanistMercurialWorkingCopy.php
+++ b/src/workingcopy/ArcanistMercurialWorkingCopy.php
@@ -18,7 +18,7 @@
     return new self();
   }
 
-  public function newRepositoryAPI() {
+  protected function newRepositoryAPI() {
     return new ArcanistMercurialAPI($this->getPath());
   }
 
diff --git a/src/workingcopy/ArcanistSubversionWorkingCopy.php b/src/workingcopy/ArcanistSubversionWorkingCopy.php
--- a/src/workingcopy/ArcanistSubversionWorkingCopy.php
+++ b/src/workingcopy/ArcanistSubversionWorkingCopy.php
@@ -70,7 +70,7 @@
     return head($candidates);
   }
 
-  public function newRepositoryAPI() {
+  protected function newRepositoryAPI() {
     return new ArcanistSubversionAPI($this->getPath());
   }
 
diff --git a/src/workingcopy/ArcanistWorkingCopy.php b/src/workingcopy/ArcanistWorkingCopy.php
--- a/src/workingcopy/ArcanistWorkingCopy.php
+++ b/src/workingcopy/ArcanistWorkingCopy.php
@@ -5,6 +5,7 @@
 
   private $path;
   private $workingDirectory;
+  private $repositoryAPI;
 
   public static function newFromWorkingDirectory($path) {
     $working_types = id(new PhutilClassMapQuery())
@@ -25,8 +26,7 @@
           continue;
         }
 
-        $working_copy->path = $ancestor_path;
-        $working_copy->workingDirectory = $path;
+        self::configureWorkingCopy($working_copy, $ancestor_path, $path);
 
         $candidates[] = $working_copy;
       }
@@ -50,7 +50,16 @@
       return $deepest->selectFromNestedWorkingCopies($candidates);
     }
 
-    return null;
+    // If we haven't found a legitimate working copy that belongs to a
+    // supported version control system, return a "filesystem" working copy.
+    // This allows some commands to work as expected even if run outside
+    // of a real working copy.
+
+    $working_copy = new ArcanistFilesystemWorkingCopy();
+
+    self::configureWorkingCopy($working_copy, $ancestor_path, $path);
+
+    return $working_copy;
   }
 
   abstract protected function newWorkingCopyFromDirectories(
@@ -110,6 +119,23 @@
     return last($candidates);
   }
 
-  abstract public function newRepositoryAPI();
+  final public function getRepositoryAPI() {
+    if (!$this->repositoryAPI) {
+      $this->repositoryAPI = $this->newRepositoryAPI();
+    }
+
+    return $this->repositoryAPI;
+  }
+
+  abstract protected function newRepositoryAPI();
+
+  private static function configureWorkingCopy(
+    ArcanistWorkingCopy $working_copy,
+    $ancestor_path,
+    $path) {
+
+    $working_copy->path = $ancestor_path;
+    $working_copy->workingDirectory = $path;
+  }
 
 }