diff --git a/server/src/email_extract.rs b/server/src/email_extract.rs
index b1210dd..42eec1b 100644
--- a/server/src/email_extract.rs
+++ b/server/src/email_extract.rs
@@ -34,6 +34,7 @@ const TEXT_PLAIN: &'static str = "text/plain";
 // Inline Askama filters module for template use
 mod filters {
     // Usage: {{ items|batch(7) }}
+    #[askama::filter_fn]
     pub fn batch<T: Clone>(
         items: &[T],
         _: &dyn ::askama::Values,