diff --git a/lib/Controller/ApiController.php b/lib/Controller/ApiController.php
index fc7d925f..55f42985 100644
--- a/lib/Controller/ApiController.php
+++ b/lib/Controller/ApiController.php
@@ -78,7 +78,13 @@ class ApiController extends Controller {
 
         // Filter only videos
         if ($this->request->getParam('vid')) {
-            $transforms[] = array($this->timelineQuery, 'videoFilter');
+            $transforms[] = array($this->timelineQuery, 'transformVideoFilter');
+        }
+
+        // Filter only for one tag
+        $tagName = $this->request->getParam('tag');
+        if ($tagName) {
+            $transforms[] = array($this->timelineQuery, 'transformTagFilter', $tagName);
         }
 
         return $transforms;
diff --git a/lib/Db/TimelineQueryDays.php b/lib/Db/TimelineQueryDays.php
index bf698aec..b5e94d44 100644
--- a/lib/Db/TimelineQueryDays.php
+++ b/lib/Db/TimelineQueryDays.php
@@ -126,9 +126,7 @@ trait TimelineQueryDays {
               ->orderBy('m.dayid', 'DESC');
 
         // Apply all transformations
-        foreach ($queryTransforms as &$transform) {
-            $transform($query, $uid);
-        }
+        $this->applyAllTransforms($queryTransforms, $query, $uid);
 
         $cursor = $query->executeQuery();
         $rows = $cursor->fetchAll();
@@ -174,9 +172,7 @@ trait TimelineQueryDays {
         $query->orderBy('m.datetaken', 'DESC');
 
         // Apply all transformations
-        foreach ($queryTransforms as &$transform) {
-            $transform($query, $uid);
-        }
+        $this->applyAllTransforms($queryTransforms, $query, $uid);
 
         $cursor = $query->executeQuery();
         $rows = $cursor->fetchAll();
diff --git a/lib/Db/TimelineQueryFilters.php b/lib/Db/TimelineQueryFilters.php
index 44e5e670..86e3ece4 100644
--- a/lib/Db/TimelineQueryFilters.php
+++ b/lib/Db/TimelineQueryFilters.php
@@ -7,14 +7,24 @@ use OCP\DB\QueryBuilder\IQueryBuilder;
 use OCP\ITags;
 
 trait TimelineQueryFilters {
-    public function transformFavoriteFilter(IQueryBuilder $query, string $userId) {
+    private function applyAllTransforms(array $transforms, IQueryBuilder &$query, string $uid): void {
+        foreach ($transforms as &$transform) {
+            $fun = array_slice($transform, 0, 2);
+            $params = array_slice($transform, 2);
+            array_unshift($params, $uid);
+            array_unshift($params, $query);
+            $fun(...$params);
+        }
+    }
+
+    public function transformFavoriteFilter(IQueryBuilder &$query, string $userId) {
         $query->innerJoin('m', 'vcategory_to_object', 'vcoi', $query->expr()->andX(
             $query->expr()->eq('vcoi.objid', 'm.fileid'),
             $query->expr()->in('vcoi.categoryid', $this->getFavoriteVCategoryFun($query, $userId)),
         ));
     }
 
-    public function addFavoriteTag(IQueryBuilder $query, string $userId) {
+    public function addFavoriteTag(IQueryBuilder &$query, string $userId) {
         $query->leftJoin('m', 'vcategory_to_object', 'vco', $query->expr()->andX(
             $query->expr()->eq('vco.objid', 'm.fileid'),
             $query->expr()->in('vco.categoryid', $this->getFavoriteVCategoryFun($query, $userId)),
@@ -31,7 +41,29 @@ trait TimelineQueryFilters {
                 ))->getSQL());
     }
 
-    public function videoFilter(IQueryBuilder $query, string $userId) {
+    public function transformVideoFilter(IQueryBuilder &$query, string $userId) {
         $query->andWhere($query->expr()->eq('m.isvideo', $query->createNamedParameter('1')));
     }
+
+    public function getSystemTagId(IQueryBuilder &$query, string $tagName) {
+        $sqb = $query->getConnection()->getQueryBuilder();
+        return $sqb->select('id')->from('systemtag')->where(
+            $sqb->expr()->andX(
+                $sqb->expr()->eq('name', $sqb->createNamedParameter($tagName)),
+                $sqb->expr()->eq('visibility', $sqb->createNamedParameter(1)),
+            ))->executeQuery()->fetchOne();
+    }
+
+    public function transformTagFilter(IQueryBuilder &$query, string $userId, string $tagName) {
+        $tagId = $this->getSystemTagId($query, $tagName);
+        if ($tagId === FALSE) {
+            $tagId = 0; // cannot abort here; that will show up everything in the response
+        }
+
+        $query->innerJoin('m', 'systemtag_object_mapping', 'stom', $query->expr()->andX(
+            $query->expr()->eq('stom.objecttype', $query->createNamedParameter("files")),
+            $query->expr()->eq('stom.objectid', 'm.fileid'),
+            $query->expr()->eq('stom.systemtagid', $query->createNamedParameter($tagId)),
+        ));
+    }
 }
\ No newline at end of file