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
@@ -482,7 +482,6 @@
     'DifferentialReleephRequestFieldSpecification' => 'applications/releeph/differential/DifferentialReleephRequestFieldSpecification.php',
     'DifferentialRemarkupRule' => 'applications/differential/remarkup/DifferentialRemarkupRule.php',
     'DifferentialReplyHandler' => 'applications/differential/mail/DifferentialReplyHandler.php',
-    'DifferentialRepositoryDatasource' => 'applications/differential/typeahead/DifferentialRepositoryDatasource.php',
     'DifferentialRepositoryField' => 'applications/differential/customfield/DifferentialRepositoryField.php',
     'DifferentialRepositoryLookup' => 'applications/differential/query/DifferentialRepositoryLookup.php',
     'DifferentialRequiredSignaturesField' => 'applications/differential/customfield/DifferentialRequiredSignaturesField.php',
@@ -827,6 +826,7 @@
     'DiffusionRepositoryEditDeleteController' => 'applications/diffusion/controller/DiffusionRepositoryEditDeleteController.php',
     'DiffusionRepositoryEditEngine' => 'applications/diffusion/editor/DiffusionRepositoryEditEngine.php',
     'DiffusionRepositoryEditUpdateController' => 'applications/diffusion/controller/DiffusionRepositoryEditUpdateController.php',
+    'DiffusionRepositoryFunctionDatasource' => 'applications/diffusion/typeahead/DiffusionRepositoryFunctionDatasource.php',
     'DiffusionRepositoryHistoryManagementPanel' => 'applications/diffusion/management/DiffusionRepositoryHistoryManagementPanel.php',
     'DiffusionRepositoryListController' => 'applications/diffusion/controller/DiffusionRepositoryListController.php',
     'DiffusionRepositoryManageController' => 'applications/diffusion/controller/DiffusionRepositoryManageController.php',
@@ -5211,7 +5211,6 @@
     'DifferentialReleephRequestFieldSpecification' => 'Phobject',
     'DifferentialRemarkupRule' => 'PhabricatorObjectRemarkupRule',
     'DifferentialReplyHandler' => 'PhabricatorApplicationTransactionReplyHandler',
-    'DifferentialRepositoryDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
     'DifferentialRepositoryField' => 'DifferentialCoreCustomField',
     'DifferentialRepositoryLookup' => 'Phobject',
     'DifferentialRequiredSignaturesField' => 'DifferentialCoreCustomField',
@@ -5575,6 +5574,7 @@
     'DiffusionRepositoryEditDeleteController' => 'DiffusionRepositoryManageController',
     'DiffusionRepositoryEditEngine' => 'PhabricatorEditEngine',
     'DiffusionRepositoryEditUpdateController' => 'DiffusionRepositoryManageController',
+    'DiffusionRepositoryFunctionDatasource' => 'PhabricatorTypeaheadCompositeDatasource',
     'DiffusionRepositoryHistoryManagementPanel' => 'DiffusionRepositoryManagementPanel',
     'DiffusionRepositoryListController' => 'DiffusionController',
     'DiffusionRepositoryManageController' => 'DiffusionController',
diff --git a/src/applications/audit/query/PhabricatorCommitSearchEngine.php b/src/applications/audit/query/PhabricatorCommitSearchEngine.php
--- a/src/applications/audit/query/PhabricatorCommitSearchEngine.php
+++ b/src/applications/audit/query/PhabricatorCommitSearchEngine.php
@@ -85,7 +85,7 @@
         ->setKey('repositoryPHIDs')
         ->setConduitKey('repositories')
         ->setAliases(array('repository', 'repositories', 'repositoryPHID'))
-        ->setDatasource(new DiffusionRepositoryDatasource()),
+        ->setDatasource(new DiffusionRepositoryFunctionDatasource()),
       id(new PhabricatorSearchDatasourceField())
         ->setLabel(pht('Packages'))
         ->setKey('packagePHIDs')
diff --git a/src/applications/differential/query/DifferentialRevisionSearchEngine.php b/src/applications/differential/query/DifferentialRevisionSearchEngine.php
--- a/src/applications/differential/query/DifferentialRevisionSearchEngine.php
+++ b/src/applications/differential/query/DifferentialRevisionSearchEngine.php
@@ -75,7 +75,7 @@
         ->setLabel(pht('Repositories'))
         ->setKey('repositoryPHIDs')
         ->setAliases(array('repository', 'repositories', 'repositoryPHID'))
-        ->setDatasource(new DifferentialRepositoryDatasource())
+        ->setDatasource(new DiffusionRepositoryFunctionDatasource())
         ->setDescription(
           pht('Find revisions from specific repositories.')),
       id(new PhabricatorSearchSelectField())
diff --git a/src/applications/differential/typeahead/DifferentialRepositoryDatasource.php b/src/applications/diffusion/typeahead/DiffusionRepositoryFunctionDatasource.php
rename from src/applications/differential/typeahead/DifferentialRepositoryDatasource.php
rename to src/applications/diffusion/typeahead/DiffusionRepositoryFunctionDatasource.php
--- a/src/applications/differential/typeahead/DifferentialRepositoryDatasource.php
+++ b/src/applications/diffusion/typeahead/DiffusionRepositoryFunctionDatasource.php
@@ -1,6 +1,6 @@
 <?php
 
-final class DifferentialRepositoryDatasource
+final class DiffusionRepositoryFunctionDatasource
   extends PhabricatorTypeaheadCompositeDatasource {
 
   public function getBrowseTitle() {
diff --git a/src/applications/diffusion/typeahead/DiffusionTaggedRepositoriesFunctionDatasource.php b/src/applications/diffusion/typeahead/DiffusionTaggedRepositoriesFunctionDatasource.php
--- a/src/applications/diffusion/typeahead/DiffusionTaggedRepositoriesFunctionDatasource.php
+++ b/src/applications/diffusion/typeahead/DiffusionTaggedRepositoriesFunctionDatasource.php
@@ -67,11 +67,19 @@
       ->execute();
 
     $results = array();
-
     foreach ($repositories as $repository) {
       $results[] = $repository->getPHID();
     }
 
+    if (!$results) {
+      // TODO: This is a little hacky, but if you query for "tagged(x)" and
+      // there are no such repositories, we want to match nothing. If we
+      // just return `array()`, that gets evaluated as "no constraint" and
+      // we match everything. This works correctly for now, but should be
+      // replaced with some more elegant/general approach eventually.
+      $results[] = PhabricatorPHIDConstants::PHID_VOID;
+    }
+
     return $results;
   }