diff --git a/scripts/arcanist.php b/scripts/arcanist.php
--- a/scripts/arcanist.php
+++ b/scripts/arcanist.php
@@ -202,17 +202,21 @@
     $workflow->setConduitTimeout($conduit_timeout);
   }
 
+  $need_working_copy = $workflow->requiresWorkingCopy();
+
   $supported_vcs_types = $workflow->getSupportedRevisionControlSystems();
-  if (!in_array($working_copy->getVCSType(), $supported_vcs_types)) {
-    throw new ArcanistUsageException(
-      pht(
-        '`%s %s` is only supported under %s.',
-        'arc',
-        $workflow->getWorkflowName(),
-        implode(', ', $supported_vcs_types)));
+  $vcs_type = $working_copy->getVCSType();
+  if ($vcs_type || $need_working_copy) {
+    if (!in_array($vcs_type, $supported_vcs_types)) {
+      throw new ArcanistUsageException(
+        pht(
+          '`%s %s` is only supported under %s.',
+          'arc',
+          $workflow->getWorkflowName(),
+          implode(', ', $supported_vcs_types)));
+    }
   }
 
-  $need_working_copy    = $workflow->requiresWorkingCopy();
   $need_conduit         = $workflow->requiresConduit();
   $need_auth            = $workflow->requiresAuthentication();
   $need_repository_api  = $workflow->requiresRepositoryAPI();
diff --git a/src/workflow/ArcanistShellCompleteWorkflow.php b/src/workflow/ArcanistShellCompleteWorkflow.php
--- a/src/workflow/ArcanistShellCompleteWorkflow.php
+++ b/src/workflow/ArcanistShellCompleteWorkflow.php
@@ -82,8 +82,11 @@
           continue;
         }
 
-        if (!in_array($vcs, $workflow->getSupportedRevisionControlSystems())) {
-          continue;
+        if ($vcs || $workflow->requiresWorkingCopy()) {
+          $supported_vcs = $workflow->getSupportedRevisionControlSystems();
+          if (!in_array($vcs, $supported_vcs)) {
+            continue;
+          }
         }
 
         $complete[] = $name;