diff --git a/src/groups/update.js b/src/groups/update.js
index 804268c587..caaedf38e4 100644
--- a/src/groups/update.js
+++ b/src/groups/update.js
@@ -77,7 +77,7 @@ module.exports = function (Groups) {
 
 		if (values.hasOwnProperty('memberPostCids')) {
 			const validCids = await categories.getCidsByPrivilege('categories:cid', groupName, 'topics:read');
-			const cidsArray = values.memberPostCids.split(',').map(cid => parseInt(cid.trim(), 10)).filter(Boolean);
+			const cidsArray = values.memberPostCids.split(',').map(cid => (cid || '').trim()).filter(Boolean);
 			payload.memberPostCids = cidsArray.filter(cid => validCids.includes(cid)).join(',') || '';
 		}
 
diff --git a/src/privileges/helpers.js b/src/privileges/helpers.js
index 6ba57cdf66..6c4e32a77e 100644
--- a/src/privileges/helpers.js
+++ b/src/privileges/helpers.js
@@ -78,7 +78,7 @@ async function isAllowedToCids(privilege, uidOrGroupName, cids) {
 	const groupKeys = cids.map(cid => `cid:${cid}:privileges:groups:${privilege}`);
 
 	// Group handling
-	if (isNaN(parseInt(uidOrGroupName, 10)) && (uidOrGroupName || '').length) {
+	if (!utils.isNumber(uidOrGroupName) && (uidOrGroupName || '').length) {
 		return await checkIfAllowedGroup(uidOrGroupName, groupKeys);
 	}
 
diff --git a/test/groups.js b/test/groups.js
index 59d88abafd..9ea3106451 100644
--- a/test/groups.js
+++ b/test/groups.js
@@ -7,6 +7,7 @@ const nconf = require('nconf');
 
 const db = require('./mocks/databasemock');
 const helpers = require('./helpers');
+const Categories = require('../src/categories');
 const Groups = require('../src/groups');
 const User = require('../src/user');
 const plugins = require('../src/plugins');
@@ -566,6 +567,20 @@ describe('Groups', () => {
 				});
 			});
 		});
+
+		it('should properly set memberPostCids', async () => {
+			const c1 = await Categories.create({ name: 'Test Category' });
+			const c2 = await Categories.create({ name: 'Test Category' });
+			const c3 = await Categories.create({ name: 'Test Category' });
+			await Groups.create({
+				name: '3rd party devs',
+			});
+			await Groups.update('3rd party devs', {
+				memberPostCids: `${c1.cid},${c2.cid},${c3.cid}`,
+			});
+			const groupData = await Groups.get('3rd party devs', {});
+			assert.strictEqual(groupData.memberPostCids, '1,2,3');
+		});
 	});
 
 	describe('.destroy()', () => {