diff --git a/src/services/ChallengeService.js b/src/services/ChallengeService.js
index 35f3d7d4..47616a6d 100644
--- a/src/services/ChallengeService.js
+++ b/src/services/ChallengeService.js
@@ -533,16 +533,12 @@ async function searchChallenges(currentUser, criteria) {
       mustNotQuery.push({ exists: { field: "groups" } });
     } else if (!currentUser.isMachine && !_hasAdminRole) {
       // If the user is not M2M and is not an admin, return public + challenges from groups the user can access
-      _.each(accessibleGroups, (g) => {
-        groupsQuery.push({ match_phrase: { groups: g } });
-      });
+      groupsQuery.push({ terms: { "groups.keyword": accessibleGroups } });
       // include public challenges
       groupsQuery.push({ bool: { must_not: { exists: { field: "groups" } } } });
     }
   } else {
-    _.each(groupsToFilter, (g) => {
-      groupsQuery.push({ match_phrase: { groups: g } });
-    });
+    groupsQuery.push({ terms: { "groups.keyword": groupsToFilter } });
   }
 
   if (criteria.ids) {
@@ -2077,7 +2073,7 @@ updateChallenge.schema = {
             .unknown(true)
         )
         .min(1),
-      tags: Joi.array().items(Joi.string().required()).min(1), // tag names
+      tags: Joi.array().items(Joi.string()), // tag names
       projectId: Joi.number().integer().positive(),
       legacyId: Joi.number().integer().positive(),
       constraints: Joi.object()