diff --git a/src/common/challenge-helper.js b/src/common/challenge-helper.js
index a7372149..062c4dbb 100644
--- a/src/common/challenge-helper.js
+++ b/src/common/challenge-helper.js
@@ -99,6 +99,10 @@ class ChallengeHelper {
 
     // check groups authorization
     await helper.ensureAccessibleByGroupsAccess(currentUser, challenge);
+
+    if (challenge.constraints) {
+      await this.validateChallengeConstraints(data.constraints);
+    }
   }
 
   async validateChallengeUpdateRequest(currentUser, challenge, data) {
@@ -196,6 +200,32 @@ class ChallengeHelper {
         `Cannot set winners for challenge with non-completed ${challenge.status} status`
       );
     }
+
+    if (data.constraints) {
+      await this.validateChallengeConstraints(data.constraints);
+    }
+  }
+
+  async validateChallengeConstraints(constraints) {
+    if (!_.isEmpty(constraints.allowedRegistrants)) {
+      await this.validateAllowedRegistrants(constraints.allowedRegistrants);
+    }
+  }
+
+  async validateAllowedRegistrants(allowedRegistrants) {
+    const members = await helper.getMembersByHandles(allowedRegistrants);
+    const incorrectHandles = _.difference(
+      allowedRegistrants,
+      _.map(members, (m) => _.lowerCase(m.handle))
+    );
+    if (incorrectHandles.length > 0) {
+      throw new errors.BadRequestError(
+        `Cannot create challenge with invalid handle in constraints. [${_.join(
+          incorrectHandles,
+          ","
+        )}]`
+      );
+    }
   }
 
   sanitizeRepeatedFieldsInUpdateRequest(data) {
diff --git a/src/common/helper.js b/src/common/helper.js
index 9a9612db..67a37435 100644
--- a/src/common/helper.js
+++ b/src/common/helper.js
@@ -1080,6 +1080,22 @@ async function getMemberByHandle(handle) {
   return res.data || {};
 }
 
+/**
+ * Get members by handles
+ * @param {Array<String>} handles the user handle
+ * @returns {Object}
+ */
+async function getMembersByHandles(handles) {
+  const token = await m2mHelper.getM2MToken();
+  const res = await axios.get(
+    `${config.MEMBERS_API_URL}/?fields=handle&handlesLower=["${_.join(handles, '","')}"]`,
+    {
+      headers: { Authorization: `Bearer ${token}` },
+    }
+  );
+  return res.data;
+}
+
 /**
  * Send self service notification
  * @param {String} type the notification type
@@ -1199,6 +1215,7 @@ module.exports = {
   cancelPayment,
   sendSelfServiceNotification,
   getMemberByHandle,
+  getMembersByHandles,
   submitZendeskRequest,
   updateSelfServiceProjectInfo,
   getFromInternalCache,
diff --git a/src/services/ChallengeService.js b/src/services/ChallengeService.js
index 15813516..336156d6 100644
--- a/src/services/ChallengeService.js
+++ b/src/services/ChallengeService.js
@@ -1167,7 +1167,7 @@ createChallenge.schema = {
       legacyId: Joi.number().integer().positive(),
       constraints: Joi.object()
         .keys({
-          allowedRegistrants: Joi.array().items(Joi.string()).optional(),
+          allowedRegistrants: Joi.array().items(Joi.string().trim().lowercase()).optional(),
         })
         .optional(),
       startDate: Joi.date().iso(),
@@ -1998,7 +1998,7 @@ updateChallenge.schema = {
       legacyId: Joi.number().integer().positive(),
       constraints: Joi.object()
         .keys({
-          allowedRegistrants: Joi.array().items(Joi.string()).optional(),
+          allowedRegistrants: Joi.array().items(Joi.string().trim().lowercase()).optional(),
         })
         .optional(),
       status: Joi.string().valid(_.values(constants.challengeStatuses)),