diff --git a/src/js/messaging.js b/src/js/messaging.js
index 33dab03c2..3094a1286 100644
--- a/src/js/messaging.js
+++ b/src/js/messaging.js
@@ -1304,6 +1304,13 @@ const getSupportData = async function() {
     }
     if ( Object.keys(addedListset).length === 0 ) {
         addedListset = undefined;
+    } else if ( Object.keys(addedListset).length > 20 ) {
+        const added = Object.keys(addedListset);
+        const truncated = added.slice(20);
+        for ( const key of truncated ) {
+            delete addedListset[key];
+        }
+        addedListset[`[${truncated.length} lists not shown]`] = '[too many]';
     }
     if ( Object.keys(removedListset).length === 0 ) {
         removedListset = undefined;