diff --git a/synapse/rest/media/v1/preview_url_resource.py b/synapse/rest/media/v1/preview_url_resource.py
index 6f896ffb5..1616809e8 100644
--- a/synapse/rest/media/v1/preview_url_resource.py
+++ b/synapse/rest/media/v1/preview_url_resource.py
@@ -74,7 +74,7 @@ class PreviewUrlResource(Resource):
         self.downloads = {}
 
         self._cleaner_loop = self.clock.looping_call(
-            self._expire_url_cache_data, 30 * 10000
+            self._expire_url_cache_data, 30 * 1000
         )
 
     def render_GET(self, request):