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
@@ -2577,6 +2577,7 @@
     'PhabricatorSpacesNamespaceSearchEngine' => 'applications/spaces/query/PhabricatorSpacesNamespaceSearchEngine.php',
     'PhabricatorSpacesNamespaceTransaction' => 'applications/spaces/storage/PhabricatorSpacesNamespaceTransaction.php',
     'PhabricatorSpacesNamespaceTransactionQuery' => 'applications/spaces/query/PhabricatorSpacesNamespaceTransactionQuery.php',
+    'PhabricatorSpacesTestCase' => 'applications/spaces/__tests__/PhabricatorSpacesTestCase.php',
     'PhabricatorSpacesViewController' => 'applications/spaces/controller/PhabricatorSpacesViewController.php',
     'PhabricatorStandardCustomField' => 'infrastructure/customfield/standard/PhabricatorStandardCustomField.php',
     'PhabricatorStandardCustomFieldBool' => 'infrastructure/customfield/standard/PhabricatorStandardCustomFieldBool.php',
@@ -6057,6 +6058,7 @@
       'PhabricatorSpacesDAO',
       'PhabricatorPolicyInterface',
       'PhabricatorApplicationTransactionInterface',
+      'PhabricatorDestructibleInterface',
     ),
     'PhabricatorSpacesNamespaceEditor' => 'PhabricatorApplicationTransactionEditor',
     'PhabricatorSpacesNamespacePHIDType' => 'PhabricatorPHIDType',
@@ -6064,6 +6066,7 @@
     'PhabricatorSpacesNamespaceSearchEngine' => 'PhabricatorApplicationSearchEngine',
     'PhabricatorSpacesNamespaceTransaction' => 'PhabricatorApplicationTransaction',
     'PhabricatorSpacesNamespaceTransactionQuery' => 'PhabricatorApplicationTransactionQuery',
+    'PhabricatorSpacesTestCase' => 'PhabricatorTestCase',
     'PhabricatorSpacesViewController' => 'PhabricatorSpacesController',
     'PhabricatorStandardCustomField' => 'PhabricatorCustomField',
     'PhabricatorStandardCustomFieldBool' => 'PhabricatorStandardCustomField',
diff --git a/src/applications/spaces/__tests__/PhabricatorSpacesTestCase.php b/src/applications/spaces/__tests__/PhabricatorSpacesTestCase.php
new file mode 100644
--- /dev/null
+++ b/src/applications/spaces/__tests__/PhabricatorSpacesTestCase.php
@@ -0,0 +1,135 @@
+<?php
+
+final class PhabricatorSpacesTestCase extends PhabricatorTestCase {
+
+  protected function getPhabricatorTestCaseConfiguration() {
+    return array(
+      self::PHABRICATOR_TESTCONFIG_BUILD_STORAGE_FIXTURES => true,
+    );
+  }
+
+  public function testSpacesAnnihilation() {
+    $this->destroyAllSpaces();
+
+    // Test that our helper methods work correctly.
+
+    $actor = $this->generateNewTestUser();
+    $this->newSpace($actor, pht('Test Space'), true);
+    $this->assertEqual(1, count($this->loadAllSpaces()));
+    $this->destroyAllSpaces();
+    $this->assertEqual(0, count($this->loadAllSpaces()));
+  }
+
+  public function testSpacesSeveralSpaces() {
+    $this->destroyAllSpaces();
+
+    // Try creating a few spaces, one of which is a default space. This should
+    // work fine.
+
+    $actor = $this->generateNewTestUser();
+    $this->newSpace($actor, pht('Default Space'), true);
+    $this->newSpace($actor, pht('Alternate Space'), false);
+    $this->assertEqual(2, count($this->loadAllSpaces()));
+  }
+
+  public function testSpacesRequireNames() {
+    $this->destroyAllSpaces();
+
+    // Spaces must have nonempty names.
+
+    $actor = $this->generateNewTestUser();
+
+    $caught = null;
+    try {
+      $options = array(
+        'continueOnNoEffect' => true,
+      );
+      $this->newSpace($actor, '', true, $options);
+    } catch (PhabricatorApplicationTransactionValidationException $ex) {
+      $caught = $ex;
+    }
+
+    $this->assertTrue(($caught instanceof Exception));
+  }
+
+  public function testSpacesUniqueDefaultSpace() {
+    $this->destroyAllSpaces();
+
+    // It shouldn't be possible to create two default spaces.
+
+    $actor = $this->generateNewTestUser();
+    $this->newSpace($actor, pht('Default Space'), true);
+
+    $caught = null;
+    try {
+      $this->newSpace($actor, pht('Default Space #2'), true);
+    } catch (AphrontDuplicateKeyQueryException $ex) {
+      $caught = $ex;
+    }
+
+    $this->assertTrue(($caught instanceof Exception));
+  }
+
+  private function loadAllSpaces() {
+    return id(new PhabricatorSpacesNamespaceQuery())
+      ->setViewer(PhabricatorUser::getOmnipotentUser())
+      ->execute();
+  }
+
+  private function destroyAllSpaces() {
+    $spaces = $this->loadAllSpaces();
+    foreach ($spaces as $space) {
+      $engine = new PhabricatorDestructionEngine();
+      $engine->destroyObject($space);
+    }
+  }
+
+  private function newSpace(
+    PhabricatorUser $actor,
+    $name,
+    $is_default,
+    array $options = array()) {
+
+    $space = PhabricatorSpacesNamespace::initializeNewNamespace($actor);
+
+    $type_name = PhabricatorSpacesNamespaceTransaction::TYPE_NAME;
+    $type_default = PhabricatorSpacesNamespaceTransaction::TYPE_DEFAULT;
+    $type_view = PhabricatorTransactions::TYPE_VIEW_POLICY;
+    $type_edit = PhabricatorTransactions::TYPE_EDIT_POLICY;
+
+    $xactions = array();
+
+    $xactions[] = id(new PhabricatorSpacesNamespaceTransaction())
+      ->setTransactionType($type_name)
+      ->setNewValue($name);
+
+    $xactions[] = id(new PhabricatorSpacesNamespaceTransaction())
+      ->setTransactionType($type_view)
+      ->setNewValue($actor->getPHID());
+
+    $xactions[] = id(new PhabricatorSpacesNamespaceTransaction())
+      ->setTransactionType($type_edit)
+      ->setNewValue($actor->getPHID());
+
+    if ($is_default) {
+      $xactions[] = id(new PhabricatorSpacesNamespaceTransaction())
+        ->setTransactionType($type_default)
+        ->setNewValue($is_default);
+    }
+
+    $content_source = PhabricatorContentSource::newConsoleSource();
+
+    $editor = id(new PhabricatorSpacesNamespaceEditor())
+      ->setActor($actor)
+      ->setContentSource($content_source);
+
+    if (isset($options['continueOnNoEffect'])) {
+      $editor->setContinueOnNoEffect(true);
+    }
+
+    $editor->applyTransactions($space, $xactions);
+
+    return $space;
+  }
+
+}
diff --git a/src/applications/spaces/storage/PhabricatorSpacesNamespace.php b/src/applications/spaces/storage/PhabricatorSpacesNamespace.php
--- a/src/applications/spaces/storage/PhabricatorSpacesNamespace.php
+++ b/src/applications/spaces/storage/PhabricatorSpacesNamespace.php
@@ -4,7 +4,8 @@
   extends PhabricatorSpacesDAO
   implements
     PhabricatorPolicyInterface,
-    PhabricatorApplicationTransactionInterface {
+    PhabricatorApplicationTransactionInterface,
+    PhabricatorDestructibleInterface {
 
   protected $namespaceName;
   protected $viewPolicy;
@@ -103,4 +104,13 @@
     return $timeline;
   }
 
+
+/* -(  PhabricatorDestructibleInterface  )----------------------------------- */
+
+
+  public function destroyObjectPermanently(
+    PhabricatorDestructionEngine $engine) {
+    $this->delete();
+  }
+
 }
diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
@@ -764,7 +764,12 @@
 
       $xactions = $this->didApplyInternalEffects($object, $xactions);
 
-      $object->save();
+      try {
+        $object->save();
+      } catch (AphrontDuplicateKeyQueryException $ex) {
+        $object->killTransaction();
+        throw $ex;
+      }
 
       foreach ($xactions as $xaction) {
         $xaction->setObjectPHID($object->getPHID());