diff --git a/src/database/mongo/sets.js b/src/database/mongo/sets.js
index e7d606092a..e12bc5caa0 100644
--- a/src/database/mongo/sets.js
+++ b/src/database/mongo/sets.js
@@ -61,7 +61,7 @@ module.exports = function(db, module) {
 			}
 
 			values = values.map(function(value) {
-				return items && Array.isArray(items.members) && items.members.indexOf(value) !== -1;
+				return !!(items && Array.isArray(items.members) && items.members.indexOf(value) !== -1);
 			});
 
 			callback(null, values);