some checks to make last admin isnt removed

public/src/forum/admin/users.js

@@ -100,7 +100,7 @@ define('forum/admin/users', function() {
 				return;
 			}
 
-			if (uids.indexOf(yourid) !== -1) {
+			if (uids.indexOf(yourid.toString()) !== -1) {
 				app.alertError('You can\'t remove yourself as Administrator!');
 			} else {
 				bootbox.confirm('Do you really want to remove admins?', function(confirm) {

src/groups.js

@@ -150,6 +150,10 @@
 		db.isSetMember('group:' + groupName + ':members', uid, callback);
 	};
 
+	Groups.getMemberCount = function(groupName, callback) {
+		db.setCount('group:' + groupName + ':members', callback);
+	};
+
 	Groups.isMemberOfGroupList = function(uid, groupListKey, callback) {
 		db.getSetMembers('group:' + groupListKey + ':members', function(err, groupNames) {
 			groupNames = internals.removeEphemeralGroups(groupNames);

src/socket.io/admin/user.js

@@ -10,22 +10,38 @@ var groups = require('../../groups'),
 
 
 User.makeAdmins = function(socket, uids, callback) {
-	toggleAdmin(uids, true, callback);
-};
+	if(!Array.isArray(uids)) {
+		return callback(new Error('[[error:invalid-data]]'));
+	}
 
-User.removeAdmins = function(socket, uids, callback) {
-	toggleAdmin(uids, false, callback);
+	async.each(uids, function(uid, next) {
+		groups.join('administrators', uid, next);
+	}, callback);
 };
 
-function toggleAdmin(uids, isAdmin, callback) {
+User.removeAdmins = function(socket, uids, callback) {
 	if(!Array.isArray(uids)) {
 		return callback(new Error('[[error:invalid-data]]'));
 	}
 
-	async.each(uids, function(uid, next) {
-		groups[isAdmin ? 'join' : 'leave']('administrators', uid, next);
+	if (uids.indexOf(socket.uid.toString()) !== -1) {
+		return callback(new Error('[[error:cant-remove-self-as-admin]]'));
+	}
+
+	async.eachSeries(uids, function(uid, next) {
+		groups.getMemberCount('administrators', function(err, count) {
+			if (err) {
+				return next(err);
+			}
+
+			if (count === 1) {
+				return next(new Error('[[error:cant-remove-last-admin]]'));
+			}
+
+			groups.leave('administrators', uid, next);
+		});
 	}, callback);
-}
+};
 
 User.createUser = function(socket, userData, callback) {
 	if (!userData) {